You should ask this on the e70 forum. We have a 2012 xdrive35d, and it's been reliable for us. Problem areas specific to the diesel are emissions equipment and injectors. ($$$). Test drive it hard, and bring a code reader to look for pending codes that don't trip the check engine light.

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2012 xDrive35d
2001 BMW X5 3.0i 5MT
and two 1987 Corvettes - Callaway Twin Turbo and Guldstrand Grand Sport 80
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