Just did my tranny (fluid & filter) and fuel filter (belly pan= PITA). 2003 3.0 140K, I used Castrol "Multi-Vehicle Automatic Trans Fluid" Full Synthetic. I read some where it is approved for BMW's....so far so good and it runs like a new vehicle.
I applied a small bead of black gasket maker and then put the new gasket on it to keep it in place. No leaks, no runs, no errors..... knock on wood! Did the same for my daughters 2002 325i 110K.