Regarding the tsb on gl5 being corrosive. .. Long resolved. No gl5 is damaging to yellow metals anymore. They are all xl8 or something like that certified. Plus the old gl5 recipe from decades ago that was corrosive was only destructive above a certain temp that most transmissions rarely reach. Main problem with gl5 today is that its additive pack makes it, in simple terms, too slippery so it doesn't allow the synchros to mesh and so down, hence poor shift quality.

Regarding synchromesh and atf, they are fine for synchro slowing down. However, my only personal issue is that that atf is on par to a 5w20 oil viscosity and synchromesh only a tad higher. 75w85 gear oil is more on par between a strait 30 or 40 weight oil viscosity. Hence makes feel uncomfortable with the thin stuff. Not saying its bad, just there are no real facts or data to verify the true lube requirements for these trannys.