Here’s the position of the tech guru from the BMW Car Club of America:
The short answer for the modern BMWs with “lifetime fill” ATF: Change it and the filter at least every 60,000 miles using ONLY the factory BMW proprietary ATF or current equivalent. Long answer: At various production dates in the mid-1990s, which vary according to model, BMW switched to their so-called “lifetime fill” ATF in automatic transmissions, as well as manual gearbox lubricant and differential oil. The reason for this, as far as anyone can tell, is marketing and not engineering – the idea being to foster the notion of the low-maintenance BMW.
There was no explanation of what “lifetime” meant, i.e., lifetime of the car, the component, or for that matter the driver. If it was the component, then obviously anything could be “lifetime fill”. The factory’s initial position was that these lubricants never need to be changed. Then, some time later, it came out that “lifetime” means 100,000 miles. Many dealerships are now recommending manual gearbox and differential oil changes be done at customer expense every 60,000 miles. Every independent BMW technician I know recommends a 30,000-60,000-mile interval, and many recommend Red Line synthetic oils, but not for automatics with “lifetime fill” – you need the factory proprietary ATF for “lifetime fill” automatics.
My inclination is to tell people to change “lifetime” ATF and filter every 60,000 miles. However I have seen BMW automatic transmissions that were maintained break anyway. In that event, say it happens at 90,000 miles, you would like to have the money you spent on the ATF and filter change to put toward your new automatic transmission. And if I told you to spend it on maintenance you’re probably not going to be very happy with me. On the other hand, I have seen maintained automatics last 200,000 miles. I have also seen un-maintained automatics last 200,000 miles, although both are very rare. There's just no predicting with these transmissions. When you choose to buy an automatic transmission, you also buy into the vagaries of the darn things, which is one reason technicians hate them. Whether to maintain a modern BMW automatic is up to you.