Don't know about the X5, but my daughter's 04 325i with 104,000 miles suddenly started using more oil than than usual, and then one day, it started spewing black smoke when she started it up. Turned out to be a bad crankcase ventilation valve (CVV), which I replaced myself, along with all the attendant hoses, for a total of about $100. Completely fixed the smoking, and I bet the oil consumption will drop to nil as well. Not sure if the X5's have a similar issue, but it's worth doing a search. Good luck.

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2003 X5 4.4i
1992 Porsche 968
2007 328i
2014 Subaru Forester XT