Few weeks ago I did front and rear diffs and transfer case. Mileage was 75k. Transfer case fluid was pretty clean. I looked around a lot and there does not appear to be any reliable replacement for the expensive BMW fluid. I went with Mobil 1 75-90 front and rear diff;s.
Mine is e90 and I did not reset anything and haven't gotten any warning lights. It's been 1k miles so far.
It's not a difficult job but it is messy and a PITA any time you have use a transfer pump
I wouldn't have done it without my friends shop lift.