Originally Posted by radi0activem
Because BMW uses synthetic ATF instead of PS fluid.
I put Mobil 1 in mine. Do it outside though because synthetic AFT STINKS!!
ATF and PSF are very similar fluids. However, ATF's tend to be a bit more robust (due to their intended use) and are oft spec'd in higher pressure systems.
A synthetic ATF like M1 ATF is a great choice and is my lube of choice for all my vehicles in their power steering systems.
Ford and Chrysler both spec ATF in their systems as well, it is quite common.