Originally Posted by c4racer

OK - now that is a loaded question

Personally I think it should be done every 50K miles. BMW used to recommend such fluid changes every 30K, then I think it moved to 45K under a Service II. Then they went to a lifetime fluid recommendation for trans and 100K for other driveline fluids. And now I think they recommend 100K, or maybe they are still lifetime - unclear to me which one actually.

I have two ZF tranny equipped BMW's that I purchased with ~90K miles on them. I am going with BMW's lifetime recommendation that was given at the time they were built. I figure if you have not changed the fluid by 60K miles you may as well not risk changing it because there will be deposits and the new fluid may very well dislodge those deposits and cause a problem. I have seen more evidence of failures from a late fluid change (ie. 75K+ miles) than from fluid going bad on a high miles transmission. Chances are something else will cause the trans to fail before the fluid ever wears out. That was the engineering behind the lifetime fluid recommendation. Now for some reason BMW may have switched to 100K fluid change, but I don't buy into that. Either change it every 50K or leave it in there, IMHO. But that's just my opinion on the matter and I'm sure for every 5 people on here you ask you will get 6 different opinions.