What is the problem when oil is leaking down in the spark plug area. on 1997 Pontiac Grand Am

Oil is on 1 spark plug more than the other 3 plugs...My dad take them out and dry them off and it will run good for about 2 to 3 weeks and then it starts to cut back really bad. (hesistating till it gets up to full speed) I just wanted to know where is the oil coming from thats leaking down in the plug area.

Asked by for the 1997 Pontiac Grand Am
I say the valve cover gaskets need to be replaced. Both of them. Yes both!