Why Is There Oil in My Spark Plug Wells?

Oil appears in the spark plug well when there is a leaking valve cover gasket or when an O-ring weakens or loosens. Each spark plug has an O-ring that prevents oil leaks. When the O-ring breaks, oil begins to pool in the spark plug well. The valve cover gasket also causes oil leaks when it is worn out or not installed correctly. Valve cover gaskets are typically mounted on top of an engine to prevent oil from leaking onto other mechanical parts, such as the spark plugs.