The oil/moisture potentially is coming from the PCV since it's plugged into the intake manifold. My concern would be how much is excessive. My 2001 Forester has 217,000 miles on the clock, and thankfully has not thrown the CEL for this yet. It would be interesting to spray some brake cleaner or some other degreaser on the old part and see if it still works.Well I got the sensor in the mail. When I removed the old sensor it looked like it was coated lightly with oil or some sort of moisture. Is that normal and to be expected with over 200k on the clock or is that indicative of another issue? I was debating whether I should just try wiping it off and putting the old one back in. But for ~$50....the new one ran fine for a minute or two without throwing a code so I'll let it be and see if it keeps up that way.