From my research, (although I have to admit I really love these cars), I would not buy a used one simply because there are some serious known issues with the N54. Oil consumption issues, and very expensive premature component failures to name some.
Anyways, I'm no expert on them either just researched them as a workmate had one for sale recently, which I ended up passing on.
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McGuyver_3 Would be the guy to talk to on this as I believe he still works at BMW and works on these things everyday.
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FD22 Good luck on your new purchase, she looks pretty nice.
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