Assuming your fuel economy is OK I would just ignore it. If you are only consuming oil at the rate you say I don't think it is motor oil. I would bet it is condensing water with soot suspended in it which resembles an oily mix. It will probably only happen in the cold if that is the case.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz