ZF (the people whg make the auto trans!) say you should change the trans fluid every 80K kms. (I think?). BMW says its a lifetime fluid. ZF calls the fluid LifeGruard.
This place sells fluid and filter service kits. I think changing your trans fluid is a good idea. Drop the AT pan and clean out all the metal and gunk in there. And then replace the filter. You will need new bolts and a gasket. The ctsc sells everything you need. Just look up your trans code on RealOEM.com (under trans menu) and then find which filter kit you need.
http://www.thectsc.com/index.php?p=c...parent=57&pg=1
There was a DIY thread for the AT in which someone bought a filter fluid kit from ctsc. Try searching for it.
Dackel