Today, I thought I would take advantage of the cool weather and clean and gap my spark plugs. I started at the front and pulled each plug, cleaned them, and gapped them. And then I got to plug six. When I pulled the plug out, the ceramic shaft was covered with oil! Not a thin coat of oil, but like I had dipped it in oil! The electrode didn't have any oil on it, so I was thinking maybe a leaking valve cover gasket? Any thoughts?

 

I'm thinking you are correct. Probably ran down into the plug well over time.