Originally Posted by GregW / Oregon
Invoice says MTF-LT-2; they say that is correct. They also say the LSD conditioner is already in it.
MTF-LT2 is the manual trans fluid, not the differential oil. The diff oil used during the 1200 mile service is the same oil BMW has been putting in all ///M cars since I have been involved in working on them. I don't have the part# handy, but it is a limited slip gear oil and is correct for the car.
If you are experiencing the grind noise during slow, tight cornering, then there is an updated fluid that can be installed to eliminate the noise from the clutches in the diff. Usually, this noise goes away as you break in the clutches. The more cornering you do, the quicker they will break-in. My E90 has never made this noise, but I have definitely broken in the rear differential
The fix is not an additive; it involves draining the current oil and filling the differential with a different fluid that contains a special friction modifier. The SI B on this subject pertains to all current ///M models ( E46,E6X,E9X and E85/86)
Oh, and I have heard this noise first hand in some of my customer's cars. It sounds like one of the rear tires is rubbing the fender or body in the rear (even though it is not). It can be pretty loud at times.
Hope this clears it up,