Transmission Output Shaft Seal Leaking

[Stevedave]

Hey, I’ve got a ‘13 FRS. The manual transmission output shaft seal has been replaced twice and is still dripping oil. First replaced on 5/18/23 and again on 8/09/23. I thought all was good until today, 8/17, when I moved the car and saw drops of gear oil on the pavement. A shop replaced it both times with OEM seals. They weren’t sure of the cause and asked that I bring it back on 8/24. I’d like to get some opinions on what might be going on so I don’t get taken when I go back.


-156k miles. I’m the 3rd owner. All adult owners and meticulously maintained
-Car is stock minus a cat back exhaust
-Transmission gear oil - Subaru High Performance Gear Oil 75W-90. Part No. SOA427V1700
-The previous owner replaced the same seal at 86k miles, ~6 years ago

The picture was taken by the shop before the first repair. I don’t have a pic before the second seal replacement, but it was no where near as dirty. The shop said that both times they checked the fluid and it wasn’t low. I have my doubts that they checked it. Shifts do feel more rough/scratchy over the last few months.
Any suggestions, questions or comments would be greatly appreciated.

[Ultramaroon]

Does the driveshaft vibrate at all? Is the sleeve yoke scratched? Is the rear output shaft bearing worn? Why is the front pipe painted? Was the car driven over anything that could have bent the output shaft?


Get the idea? Many possibilities.

[Stevedave]

Driveshaft doesn’t vibrate. It sometimes clunks when I put it into first gear. I haven’t driven over anything that may have bent it. I believe the leak was there when I bought it 4 months ago. Paint, not sure. It was undercoated 6 years ago when the previous owner bought it from TX and brought it back to IL.

Sounds like I’m at the shop’s mercy, or perhaps another shop’s opinion is needed. During the first seal replacement, they didn’t look for any reasons of failure. Same with the second time, which I thought was weird. I wasn’t charged for the second replacement.

I can do straightforward DIY stuff, but troubleshooting this is likely beyond me. They said they didn’t see any other issues was to why it would be leaking.
Here are more pics from the first service.

[Ultramaroon]

It's not terrible. I missed a fleck of sawdust trapped in the seal once when installing a replacement transmission. OMG, what a horrible mess that was.

[soundman98]

why does the transmission mount appear wet?

if i'm looking at the pictures correctly, the left side is the front of the car, correct?

usually a rear main seal would create a wet u-joint assembly. in this case, the transmission looks wet leading up to the rear, but the u-joint looks dry, indicating to me that the leak is ahead of the rear main seal.

normally vehicles are travelling down the road as they leak, so the leak is pushed backwards from the point of origin by the air flowing around everything. unless you drive backwards everywhere!

[Stevedave]

Originally Posted by soundman98

why does the transmission mount appear wet?
I’m not sure. The previous owner was detailing the car when I arrived to look at it. They had just finished detailing and spraying down the engine bay. Could any grease or oil have worked its way down? It had a leaky hydraulic clutch hose that was replaced at the same time as the transmission seal.

if i'm looking at the pictures correctly, the left side is the front of the car, correct?

Correct



usually a rear main seal would create a wet u-joint assembly. in this case, the transmission looks wet leading up to the rear, but the u-joint looks dry, indicating to me that the leak is ahead of the rear main seal.

So possibly an oil leak from the engine working its way back? Something like a timing cover leak?



normally vehicles are travelling down the road as they leak, so the leak is pushed backwards from the point of origin by the air flowing around everything. unless you drive backwards everywhere!

Are you thinking the leak is not transmission related? More specifically, nothing to do with the output shaft seal? In this case, would it be worth having a dye test done to see if the engine’s leaking oil?

[Ultramaroon]

Originally Posted by soundman98

why does the transmission mount appear wet?

if i'm looking at the pictures correctly, the left side is the front of the car, correct?

usually a rear main seal would create a wet u-joint assembly. in this case, the transmission looks wet leading up to the rear, but the u-joint looks dry, indicating to me that the leak is ahead of the rear main seal.

normally vehicles are travelling down the road as they leak, so the leak is pushed backwards from the point of origin by the air flowing around everything. unless you drive backwards everywhere!

Oh, maybe the case vent valve is broken, or something else is loose. Gear selector shaft seal?

[soundman98]

Originally Posted by Stevedave

So possibly an oil leak from the engine working its way back? Something like a timing cover leak?

it shouldn't be a timing cover leak-- that would be at the very front of the motor-- any mechanic should be able to easily identify that, as the whole motor and trans would be wet.

i think ultra's thought of it being either a broken trans vent is on track, or possibly an over-filled trans. though in his picture, the neutral safety switch is on the same side as your pictures-- it could also be a failed switch allowing oil to pass by it.

Originally Posted by Stevedave

Are you thinking the leak is not transmission related? More specifically, nothing to do with the output shaft seal? In this case, would it be worth having a dye test done to see if the engine’s leaking oil?

very first thing to remove any further speculation, i would clean the transmission off of any current oil/wetness, and run a hand over hte suspected trouble spots feeling for lost/damaged/broken parts.

of course, it won't be fun getting under the car, and hosing it down with engine degreaser, but the first step in any leakage issue is to verify that the indications of a leak are a real and current problem, and not a past previously-corrected-but-not-cleaned problem, or even something as simple as a one-time over-fill event.

from the pictures provided, it just doesn't look like a rear main seal to me, unless you spend a majority of time driving the car backwards.

[Stevedave]

Originally Posted by Ultramaroon

Oh, maybe the case vent valve is broken, or something else is loose. Gear selector shaft seal?

From what I’ve read, it doesn’t sound like the case vent valve is removable. Is it possible that it’s serviceable and not removable? It’d be nice if replacing it is an option, and is an easy swap like the pressure relief valve on the differential.

If I’m going to be under the car, degreasing and cleaning everything up, might as well swap that out as a process of elimination. That is if it’s an inexpensive part and easy to get to.

[Stevedave]

Originally Posted by soundman98

it shouldn't be a timing cover leak-- that would be at the very front of the motor-- any mechanic should be able to easily identify that, as the whole motor and trans would be wet.

OK. That makes sense.

i think ultra's thought of it being either a broken trans vent is on track, or possibly an over-filled trans. though in his picture, the neutral safety switch is on the same side as your pictures-- it could also be a failed switch allowing oil to pass by it.

I replaced the following fluids shortly after I got the car - transmission, differential and oil. I refilled the trans fluid until it came out the fill hole and waited a good hour before pitting the plug back in.

The failed switch is an interesting suggestion. I’ll read up on that. That makes sense as the shop has said the fluid level was fine both times they replaced the seal.

very first thing to remove any further speculation, i would clean the transmission off of any current oil/wetness, and run a hand over hte suspected trouble spots feeling for lost/damaged/broken parts.

I will get to this this week and report my findings

of course, it won't be fun getting under the car, and hosing it down with engine degreaser, but the first step in any leakage issue is to verify that the indications of a leak are a real and current problem, and not a past previously-corrected-but-not-cleaned problem, or even something as simple as a one-time over-fill event.

This is a logical approach. I’m curious why the shop just threw another seal on it, said they cleaned it up and to bring it back on 8/24. Seems like they should’ve done troubleshooting and diagnosing at this time.

from the pictures provided, it just doesn't look like a rear main seal to me, unless you spend a majority of time driving the car backwards.

I didn’t notice any leaks on the concrete until the mentioned dates in the original post. Here are a couple pics to show how much is dripping. That’s a quarter for size reference. Both pics are from the car parked in two different spots after two separate drives a few days apart as it’s not my daily.

[Stevedave]

Here are the pics. Didn’t upload on previous post.

[soundman98]

that could easily be residual oil dripping off. definitely clean first, and monitor.

[Ultramaroon]

Originally Posted by Stevedave

From what I’ve read, it doesn’t sound like the case vent valve is removable. Is it possible that it’s serviceable and not removable? It’d be nice if replacing it is an option, and is an easy swap like the pressure relief valve on the differential.

If I’m going to be under the car, degreasing and cleaning everything up, might as well swap that out as a process of elimination. That is if it’s an inexpensive part and easy to get to.

Safe money's on the gear selector seal. Nothing else really moves. I was just musing over other possible leaky points. I had to replace a failed check on a different beloved shitbox many years ago. I think soundman's right. Rear seal looks ok.

[Stevedave]

Originally Posted by soundman98

that could easily be residual oil dripping off. definitely clean first, and monitor.

Ok. Since it’s been cleaned off twice, the seal replaced twice and doing this since I got the car in April, I’m thinking I’ll take it to the free follow up inspection on Wednesday. See what the shop has to say. I’ll ask to look at it while it’s on the lift and take some pics.

Would you still recommend not going forward with anything other than having the tech clean it all up?
Anything I should specifically mention to the tech while it’s there? I don’t want to be a jerk, but maybe asking if they’re cleaning everything up, not just around the seal.

It’s frustrating as my mechanic of 20+ years retired and I’m having a hard time finding a good shop in my area. A few people in the car community has said this shop is decent. So, I’d like to tread lightly.