I would like to change the gear lube in the transfer case and two
>differentials in my 2001 BMW 330XI.
>
>What brand; type and viscosity should I use?
>
>What quantity should I order and from whom?
>
>Thanks much.
The owner's manual will tell you all of these things. I highly recommend following it exactly because the controlled-slip stuff requires pretty precise shear characteristics of the oil. I'll say that I have never gone wrong with either Red Line or Royal Purple stuff, though I suspect the Red Line is recommended.
--scott