Anton, I'm currently runnunt Redline MTL in my 6-speed (oops, mistakenly said MT-90 in an earlier thread.) I switched from the regular ATF that some folks use to the MTL for better shifting at low temperatures. This has generally worked well....but...I have found that my 2nd gear synchro is not as smooth as I would like (better than with ATF. but still not as smooth as 3rd+) I am going to give the MTL half the winter to see how I like it when the temp drops, and may swap it out for Mobil SynATF. Part of my issues with the MTL may be that it is actually a bit TOO slippery and doesn't let the synchros match gear speeds at an optimum speed. The flip side is that MTL is excellent lub for the bushings and bearing that are found inside any transmission. You can find more info on Redline MTL with this fact sheet or get general information at their product page.
Cheers,
Duey