Your comment brings up a point I'd been grappling with but decided not to post above: unless you are a tribilogist with particular experience with the base properties of the ATF fill, it is hard to glean info on the fluid itself and it's relative degradation. There are many people who 'know' motor oils; many that know Mobil 1, or Green Castrol or whatever... but when it comes to the BMW fill for their ATF the universe of shared knowledge becomes much, much smaller. UOAs without someone to interpret can be useless, or misleading.

I've worked with Terry Dyson in the past (Dyson Analysis)- dunno what he knows about this, for all I know he'd say "oh sure, thats a XXX, with a YYY and they use some ZZZ as well- just run a UOA on a fresh bottle and we can tell you what's going on".

Finally agree that ZF knows way, way more than we will ever know- and will not tell us.

A