oil

[Importroller]

if there is oil on the spark plug threads but not on the electrode, what would this be in indication of what has gone bad?

[benemorius]

If you're sure it's only on the threads, check for oil leaks on the outside of the engine. Could be the valve cover gasket leaking oil down to the plugs. If you don't see anything, clean up the oil and wait and see if it reappears. If it doesn't, I'd just forget about the whole thing.

[navysnail]

very likely its the inner valve cover gasket, as that is the only way that oil could get on the outer part of the spark plug, and by outer i mean the part that is not in the head.

[DriftingXJDM]

if its on the spark plug area remove and replace your spartplug tube seal... should be a whole piece