I didn't know I had the 6 until about a week after buying my X. The PO debadged the car. Doesn't even have X5 badge. After reading up on the reliability of the M54 vs M62 and N62 I felt like I won that dice roll.
I've personally done the M62 chain guide job twice I wouldn't be afraid of that engine, but with the N62 I would want to make sure it wasn't in the range of iffy intermediate lever

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)