Thanks for the write-up.
I did the tranny oil change on my 525i with 66K miles last weekend. The old oil was black, magnets looked like sponges and I replaced the filter as well.
I used Castrol Multi-Import ATF and so far so good.
My only concern is about the correct ATF level. I ended up adding ~6.5 quarts of new ATF into the tranny.
Anyway, I plan to do the drain/refill next weekend as soon as I receive the 14mm hex bit that I ordered to do the differential oil change.
None are more hopelessly enslaved than those who think they are free.