oil on threads of 1 spark plug

[naphets]

I have a 2006 Chevrolet Aveo Special Value 4 Door Sedan
Yesterday I changed my serpentine belt, without an issue. Then changed my spark plugs with some NGK Iridium, and to my disappointment I found oil on one threads of one of the spark plugs!!!
I have roughly 125,000 miles and was expecting to do my timing belt this week, and my brake pads and shoes, and sock absorbers and struts and bearing plates. but now I believe I may have a lot more work to do!!
The question is, what is it that I have to do? Pull one piston? Rebuild? what options do I have
What parts do I need to rebuild and what are the best parts to get, and where is the best place to get them?

[zmatus]

Just go and replaced the valves top cover gasket.

[FyrFytr]

Bump on old thread. found oil on my plugs today. How do you replace the top cover gasket?

[t.fader]

gasket is 35$, i had a friend do mine, hes a mechanic, would have cost 235$ from gm, took about 1.5 hrs cause it has to dry, then u gotta make sure it doesnt leak after wards/

[snrusnak]

What do you mean it has to dry? is it an RTV sealant type gasket? My wife's is leaking pretty bad, every oil change (~5k miles) I pull the wires and there is a lot of oil sitting in the galley around the plugs. I am going to change it soon (with plugs and wires too) but want to make sure it is straight forward. I am very mechanical, but don't understand why it "has to dry"...