[SockMonkey]

So I picked up a '13 BRZ with 59k miles a few weeks ago, obviously outside the 5yr/60k drivetrain warranty. After getting use to the car I started to notice a crunch/grind when I was shifting 3rd to 4th at higher rpm, like a highway on ramp. After some googling I found this was/is a some what common problem, usually fixed be replacing the tranny. I figured it needed a fluid change, but remembered the previous owner saying they had it serviced last year. I got him to send me the invoice and it says 3 quarts of "SOA427V1700 HIGH PERF GEAR OIL 75W-90". When I google that, I find that it is Subaru's oem oil and it is a GL-5 gear oil. Everything I read says these transmissions should only ever have GL-3/4 because GL-5 fluids have sulfur and phosphor additives that are bad for the synchros. This was done at 51k, 8k miles ago.

I was originally planning to change the fluid for some redline MT-85 or 90. But before I do that, would I have any grounds to pursue repair/replacement from Subaru? Could having that gear oil in there for 8k miles have caused this crunch I'm experiencing from damaging synchros?