Regularly fluid changes, say 20-30-40k are essential. But once the damage is done and crud is present, your options become limited.
A passive drain and fill should be fine- just get new fluid in there. (Why do forums go nuts about "I change my oil every 5k" and "I change it every 2500", yet they all blithely leave the ATF sit for YEARS!)
People give BMW engineers' way too much credit... they (the bean counters) don't care at all about the tranny, they don't want to pay for a change under either the 50k maintenance or 100k extended maintenance....
It is laughable that people actually think they are getting technical advice from Consumer Relations....