Subaru Repair: 03 subaru outback wagon, valve cover gasket, subaru outback

Question
there is engine oil in the recess where the spark plug goes and the engine is missing on that cylinder.(rough and bucking) how did it get in there and what do i do to fix it?

Answer
What happens is between the cylinder head and the valve cover there is a gasket. In each spark plug hole there is an o-ring which has a tendency to leak. The only way to remedy the problem is to replace the valve cover gasket. The o-rings come with the kit.