Oil on the bottom of the oil pan
 

After replacing all the usual seals (cam cover gaskets, half-moon, cam chain tensioner, cam cap) on both banks of my '01 2.8L -- twice -- I still have oil dripping from the bottom of the oil pan. I'm almost certain that I've stopped the cam cover leak, as there is no more burning oil smell and the exhaust headers are bone-dry. I've felt all around the upper side of the oil pan an there's no oil there -- I really don't think there's a residual leak that's dripping on the oil pan from somewhere above. So that leaves the drain plug and the sensor. I don't think it's the sensor because there's no oil in the cavity where it sits -- so that leaves the drain plug. But it's definitely not cross-threaded and I've changed the copper washer at least once. Am I missing something? The washer is supposed to fit my engine, but I'm wondering if the inner diameter is too large?