SeT

I own a '07 Scion tC nearing 150k miles. I had my check engine light come on today. I happen to have an OBD reader so I checked it out. I'm getting misfires on cylinders 3 and 4. I do most of my own maintenance and repairs, the plugs and valve cover gasket was replaced about 15k miles ago. The valve cover gasket I replaced due to a small leak which stopped after replacement. I pulled everything apart to make sure I didn't screw up somehow, the gasket seemed to be seated fine. When I looked at the plugs, however, there was quite a bit of oil on the electrodes. Any suggestions what could cause this so I can avoid a costly visit to a mechanic?

criminaltc

Yep, two things cause oil on the spark plugs. Valve cover gasket and spark plug seals. Replace the seals and make sure you have the valve cover gasket good for sure.