I stumbled across this thread recently and found it to be quite informative. It specifically discusses oils for the S52, but according to the referenced TIS the M42 and M44 engines are also considered to require "special oils". I'm going to be switching to Shell Rotella T 5w40 on my next oil changes based on this and other information I've seen.
http://forums.bimmerforums.com/forum....php?t=1003372