I've never seen a stock airfliter have black oil trapped in.It was across the edge of the foam next to the battery and elswhere. Where would oil come from? I've hardly driven much in the rain. Truck has 12000 miles on the original filter and the gauge was down about a 1/4 from the top. Had the hard starting problem fixed and the fuel filter changed recently. What high flowing particulate trapping filter would not void the warranty.

 

Does it look like oil or black road grime?

I have seen mine where it's more like black road grime.

TOny

 

Ditto on that .... probably the magnesium chloride de-icer adds some, too.