Oil only on THREADS of plug

[J90GT]

Well heres the situation, car runs strong put up decent #'s on the dyno, no missing, no smoke nada only problems, it runs rich.


Everything has been replaced,wires,cap,rotors,coil etc etc. i go to check my plugs and #5 cylinder has oil on the threads but NOT on the "electrode" or prong just the threads. I found this kind of strange so i cleaned the plug went out for a quick spin and came back, pulled it. Again oil on just the threads.



Any ideas, why oil is just on the threads? i would think if i had bad rings the whole plugged would be covered?

 

[5.0tbirdguy]

Could be valve seals. The intake seals will leak when you idle or close the throttle. If it smokes when idling for 15 minutes the valve seals are bad for sure.