Never had an X5M so can't speak to that particularly.

But for BMW transmissions, specifically the ZF ones, like in the 4.8is and I think all newer (2006+) BMWs... make sure the fluid and filter has been part of the service schedule. BMW screwed future owners after owner 2 (warranty period) by stating the trans is lifetime fill. Causes many trans issues and outright failure leaving the original fluid. ZF recommends 60,000-80,000 miles depending on driving style.

After having to replace the transmission on our 2010 E70 diesel... I've serviced every one of our BMW's trans to avoid that ordeal again. Recently did our E53 4.8is @ 126k miles and it cured the 2-1 gear change slam and some delayed gear changing. Feels like a new vehicle now.

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2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)