Any ideas?

[Shortcut]

Non issue

 

[StuP]

I had the same year / engine, but never had that problem. Was it a water oil mix, or one or the other. Its got to have come from somewhere, if it's oil it should be traceable.

 

[medium187mph]

Valve cover seal is damaged...

Oil on plugs is a common indication but I’m not a mechanic.

 

[Ghost941]

Valve cover seal is damaged...

Oil on plugs is a common indication but I’m not a mechanic.

Beat me to it. Most likely culprit from my limited experience.

 

[3clicks_Off]

was the crush washer on the spark plug intact?
I have seen them split but only on small engines line a 2 stroke boat motor or dirt bike