Originally Posted by HPIA4v2

I use Dextron III for my xfer case. Maybe the trace of fluid is just from last flush.

Yes I always use BMW brake/coolant.
As far as diff, I stick with 75-90 Redline/M1/RP and leave the heavier weight for LSD (limited slip diff) kind, but I doubt it'll do any harm with you go with heavier oil on your X5.

Welcome to the board.