I think it's a toss up, on the tranny. You should be fine and with Xoutpost you can do most of the repairs yourself. $ 2400.00 will buy you alot of parts and it sounds like you are willing to work on your X. Enjoy your X. I find the harder you drive them the longer they last.

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2010 X5M /// R63 AMG...Wifey's 540HP Family Hualer

2001 X5 3.0i Sport 335,448 miles & counting...
SMG M3 Steering wheel
E46 Stainless Racing Headers
4.6is Exhaust
Turner Pulleys
Afe Intake
Brembo drilled rotors
PowerFlex Bushings
Hualingan
30mm H&R Spacers rear
20mm H&R Spacers front
Bavarian Autosport High-Performance Coils
Active Autowerke's Performance Software