My father owns a 2002 SAAB. He said oil is on one of the spark plugs. on 2002 Saab 9-5

This plug also seemed striped out so he installed a heli coil. This is the only plug with oil on it. I would think it would be a cylinder problem but I am not sure? Can you assist me? Thanks Derek

Asked by for the 2002 Saab 9-5
poss valve cover gasket seal at plug o ring