I changed the spark plugs on my Fun pickup a couple of weekends ago and while most were healthy there was oil on the number 1 spark plug.

What is the likely cause of this? is it a problem? and is it hard to fix?

TIA

Was it on the end of the plug in the cylinder on around the outside?

Quite often the end of the cam cover gasket leaks down onto the end of the plug.

Was it on the end of the plug in the cylinder on around the outside?

Quite often the end of the cam cover gasket leaks down onto the end of the plug.

I noticed it on the thread of the plug

Probably running down from the cam cover then matey, a new gasket isnt much.

Ok, thanks.