If you find oil on a spark plug, on the spark plug threads, or in the spark plug well, oil is leaking from the spark plug well gaskets. Oil collected in the spark plug well, also known as the spark plug tube, is a problem since it can pile up on the ignition coil and spark plug until it causes runability issues and possibly a check engine light. This post covers the signs of a spark plug tube gasket leak, why oil would cover a spark plug or ignition coil, and how you can fix it.