Time for a new valve cover gasket! Same thing happened when I changed mine.They made a scary crunching noise when I took them out ... I thought I stripped the threads!
Wasn't that bad actually, by far the easiest spark plug change I have ever done! The car idles much smoother now and I have a lot of power back under 3500RPM. There's a hill that I used to be able to go up in 5th gear that I had to downshift the last year or so. Now it seems to have all of it's power back.
Only concerning thing was the spark plug wells for cylinders 2 and 3 were filled with oil. Blew out a puff of smoke on startup!