oil on spark plugs

Typically caused by worn rings or valve guides/seals. Lots of miles on vehicle?

Its a simple fix. Get yourself a Valve cover gasket set that includes the "spark plug gaskets". Remove your valve cover, remove old gasket and spark plug gasket, clean it up, put new gaskets in and bolt it back up in the right sequence to torque spec(dont overtighten!). If you look around online you can find more detailed information on this subject. I just fixed this problem on mine recently.