https://www.bimmerforums.com/forum/s...l-after-5k-rpm
https://forum.miata.net/vb/showthread.php?t=507918
https://forums.nasioc.com/forums/sho....php?t=2088183
This seems to be a thing that, until tonight, I've never heard of. I also call bullshit on all the theories about leaky slave and air.
I think it's kickback but I don't know why.
I suggest having a friend rev it for you while you actually have hands on the fork. If it's kicking back you WILL be able to:
1. With the engine off, simulate it and get a feel for how much it's kicking back by just squeezing the fork by hand.
2. Measure it by being clever with a caliper.
3. Reproduce it by revving the engine in neutral at a standstill.
This is brand new to me. I can only tell you what I would try. All of your previous observations are spot on. I was an idiot for skimming over it.