I always thought we had the 420G in our cars.Same tranny in the M5 and 540i with maybe a few changes in the M5.
RP has proved itself over the years and the MTL Redline has been in quite a few cars I know for over 60K and the tranny still works.I remember a concoction from UUC ( the mixing of two different fluids ) to supposedly get rid of the Light weight fly wheel chatter,I think it was UUC.
I am putting synchromax in my car here soon to see what happens,a bunch of people like it.
The 420G is a pretty notchy tranny to begin with or at least everyone I have driven has been very distinctive in it's shifting of gears.
Getrag type D = Getrag type 226 = BMW S6S 420G
Assuming the fluid is proper type (and reasonable condition with less than 50K mi on it) and level not low, notchiness results from wear or bent/distorted parts. This damage can sometimes be masked or managed with certain fluids, but the transmission is already degraded to some degree. When notchiness and baulkiness become serious, the linkage and associated synchro assemblies can bind and fail from wear and/or high shifting force. The wisest thing to do with a notchy tranny is change the fluid often using proper lubricant and shift gently or skip gears when it's behaving badly. When the problem becomes chronic or you get tired of babying it, you should have it rebuilt to address the design issues instead of busting metallic parts which often find their way through the gearsets and destroy them. I occasionally rebuild, upgrade and modify these trannys for racers. It is possible to optimize shift quality and fully correct the design weaknesses that cause such issues. This allows the tranny to be shifted quickly and aggressively without fear and you can run factory fill that ensures long gearset lifecycle without such symptoms. Selecting aftermarket fluids that minimize shifter notchiness is not the most thoughtful approach for maximizing lifecycle of shafts, gearsets, bearings, synchros etc.
