I'm noticing a small amount of oil on top of the head. I'm not sure if it's leaking from the spark plug hole or from the head bolts. I know with basic engine mechanics, you're supposed to only hand tighten the spark plug. Should I maybe tighten the plug with a wrench a little more or maybe the head bolts? It's hard to tell exactly where the oil is coming from, but being that it's on top of the head I figure it can only be coming from one of those two areas.