BMW used to use MTF-LT-1, which was essentially a 7.5cst (DexIII viscosity) oil, which was later replaced by MTF-LT-2 (which was thicker), but claimed backwards compatiblity to MTF-LT-1 apps. There was recently a post on this site by someone who suggested that MTF-LT-3 is now the factory fill for the E90 manual transmission, and I have no clue if that fluid is similar to the MTF-LT-2 or MTF-LT-1 fluids at all. I'll be checking with the tech depts at Redline and Royal Purple to see if it is similar to the MTF-LT-1.
People on the M5boards have used Royal Purple Synchromax in place of the MTF-LT-01, and others have used Redline D4 ATF in place of it. D4 ATF works well but appears to require replacement every 15K or so to maintain good shift quality. Then again, I'm not sure if a MTF-LT-1 "like" MTF can be used safely in the E90 transmissions because it now uses MTF-LT-3 supposedly, so I'll be checking with the people at Redline and Royal Purple.
For fun, I decided to make a comparison of the fluids (OE MTF, RP Synchromax, MTFGlide, and D4 ATF). Note, that this is probably not the best way of comparing the fluids, but its worth looking at:
