Scotty I have a Ford crown Vic 2009 4.6 engine, and I have oil getting on the spark plug in cylinder 5.the engine starts shacking and bumping, and the rpms will drop when it bumps. When I clean the oil off it will be ok for about 2 days, and the problem comes back and I have to clean oil of the spark plug again. Why do you think oil is leaking on the spark plug? The engine light doesn't come on cuz of it.

if top and bottom of the plug is covered with oil, replace the seal on the spark plug tube and gasket. If just the firing end, engine is worn out and oil is pouring inside from worn engine parts meaning it needs a rebuild