Originally Posted by SenorFunkyPants
There are around 10 different makes of oil certified for use in this diff, but the one quoted in the Service bulletin is Castrol SAF-XJ which contains friction (slip) modifiers. It is this oil that is regarded as being the most effective are resolving the noises made by the diff clutch pack.
Actually, that is not correct. The SAF-XJ oil is the regular oil that is specified for use in the M3 as well as just about every other newer BMW. This is the oil that would be used during the 1200 mile run-in service. This is technically a "limited slip" oil. This oil is part# 83 22 1 470 080.
There is a special differential oil that is available to reduce clutch noise on the M models. This is the oil that we have been discussing in this thread. The part# is 83 22 2 282 583. It comes in 3 small bottles and is only used when a grinding/rubbing noise is reported. The regular XJ oil is drained and this oil is installed.