Automatic Transmission Fluid (ATF) and Filter ?
 

An interesting article:
Bimmerforums - The Ultimate BMW Forum - View Single Post - Auto Tranny Lifetime Fill = LOL

I'll agree with some of the items in that article, but only to a point.

First, I have an E39 528, one of the BMWs with the clunky GM trans. My father bought it new and maintained it by the book at his dealer. When I bought it from him 3 years ago, at 92K miles, it had never had a trans service done. So I had the trans fluid and filter changed at a local indy with lots of BMW experience. I frankly don't even know what fluid they used, just trusted them to do it right. Here we are 3 years later and it works just fine, but there was absolutely no change in how it shifted. So much for the "if it's past 50K don't let the magic out."

On my X5, I've asked my dealer twice in the past year to service the trans and they won't do it. And as recently as 3 months ago they again said no, said that BMW tells them not to service the automatics. If they do and the trans fails, customers will hold BMW liable for the trans failures. How's that for convoluted logic. So since I tow a race car trailer all over the eastern US, I guess it's back to my indy and have him do the trans for me. Just need to figure out what fluid for this trans.

You are confusing causing failure with increasing the odds of failure. Transmission fluid changes increase the risk of failure, they don't necessarily cause failure. So, your sample of one that didn't cause a failure is completely as expected; most transmissions don't fail. There is an increased risk, but it is still a small percentage. It is not correct to extrapolate your experience and say that therefore changing the transmission fluid at high mileage will never cause a failure.

I agree it's just a single data point. However, it really depends on who you ask. I had a conversation with a ZF technical rep a couple years ago related to the tiptronic trans in an Audi and a Porsche Boxster (same basic trans and they even share case parts). His recommendation was to change fluid, period. The only time changing atf at 80, 90, 100K miles was a problem was if the trans was already going bad, the detergents in fresh fluid might accelerate the failure. But if the trans was fine, there's no reason to not change fluid. At that time I had 75K on my Audi and he said go ahead and change it. In fact he said I'd be crazy to not change it if I wanted to keep the car for a while. Unfortunately I can't say if it would have affected long term reliability, the car got rear ended and totalled a few months later.

I guess the real solution is to not wait until 40 or 50K to change the fluid and filter, and just make it part of the 30K service intervals. Now if I could only convince my dealer to do this for the X5, I'd be a happy camper.

I would say that a fluid change on a high-mileage transmission for the first time increases the odds, to an unknown extend, of immediate failure, but decreases the odds of a longer-term failure down the road.