Had my E53 back for about three weeks now following a transmission rebuild. It's fitted with the same 6spd auto that the V8 4.8 has. The failure occurred at 41,890 miles and was nothing to do with the fluid - changing it would have made no difference.

The failure was within the torque converter and not the actual transmission but the broken plastic (yes plastic!) parts from the TC were ingested by the tranny oil pump destroying both it and the downstream clutches when the pressure failed. There were no warnings at all. There is no doubt that this was a premature failure and just 'one of those things' that can happen. Not that BMW GB showed any inclination to 'goodwill' the repair though!

However, this failure is not unusual and occurs on other vehicles that use the same box (Jaguar & Range Rover I'm told), though it is rare at low mileage like mine. Auto transmissions generally have a higher failure rate because they are by their nature a more complex beast. They are also much more expensive to fix - albeit with a rebuild costing approx 1/3 of a remfctrd and BMW fitted unit. Whether the transmissions fitted to the X5 are any better or worse than those used by other manufacturers depends upon the actual number of failures, and failure modes. Percentage wise it's probably around average. Perhaps an FOI request to BMW NA may reveal the true nature of the number of failures - but that might only identify those BMW know about. It won't pick up those fixed by other specialists - as mine was.

Given the option again, I would have had the 6spd manual but they are very difficult to sell on (and go for a lower price) as no one wants a vehicle like an X5 with a manual gearbox.

__________________
Me:
Current: 2011 E71 40D Vermilion Red/Beige Nappa

Wifey:
Current: 2012 R80 Countryman SDX Green/Cream