What I've gathered off forums and from Roundel is that there's no guarenteed way to break or save your automatic gearbox. Some will fail at 80k even though the owner did a 50k mile flush. Others have run to 200k. But it's safe to say that most of the ZF and GM automatics tend to go around 90-120k miles. Just start saving up some money every week to prepare for the inevitable.

My next BMW will be a manual