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When replacing the spark plugs, they were coated with oil

Q: When replacing the spark plugs, they were coated with oil. When I unscrewed them, I think that oil flowed into the cylinder. Did this damage anything like my catalytic converter?

A: Oil in the spark plug wells is due to bad valve cover gasket seal, particularly the (usually) separate round gaskets around each spark plug well. Oil will attack the rubber high voltage wire boot over time, and will eventually cause misfire. If you are working on an old car, or a car you know will have a lot of oil in the well, you can carefully suck it out with a syringe attached to a thin tube.

To the best of my knowledge, the oil will be burned in the cylinder before it is pushed out the exhaust valve. This will develop soot, but it should not damage the catalytic converter if it is done just on that seldom occasion. But you should replace the valve cover gasket because it is the cheapest solution.

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