It's been a source of discussion for years
First, I don't think you'll see any performance improvements from changing transmission fluid. It's common knowledge, BMW says their fluid is lifetime. Perhaps that's legitimate, perhaps is related to the fact that they have a maintenance free program for the first 50k miles and with fluid at $25 per liter, the cost would add up pretty fast.
I think the consensus is that you can't harm the car by changing the fluid. I would definitely change it at 75-100k miles but it's not something you have to do with the frequency of an oil change.
I just changed the fluid in my M5 this spring and will probably change the fluid in my X3 next year.
The next big discussion topic is always what to use for fluid. Many like Redline, Mobil1, and Royal Purple. Rather than losing any sleep over it, I chose to go back with the OEM fluid. I probably wouldn't go to the effort of trying to change the filter unless I were going into the tranny for maintenance reasons.
Last edited by bimmernut1; 09-05-2010 at 10:28 PM.