oil on plugs, Camry

Hey my GF has a '92 Toyota Camry, I changed the plugs on it and they looked old, 2 of them had oil on the threads and slight oil stains above the nut on the plug.

I'm new on this Toyota but read some info about the spark plug tubes(threaded into the head) and seals(at the top of the tubes by the VC). They can leak and fill the tubes with oil. I did not see any oil in the tubes, maybe residue(its dark in there). the car does not burn any oil or smoke.

Anyway I would think if its on the threads then its coming from the valve seals or past the rings. Or could oil thats puddled in the tubes seep down to the threads from up top? Like I said the plugs were old so maybe it had this common oil in the tubes at one point and then they fixed it.

So I'm not sure if this oil is just lingering from a previous issue that has been fixed or if its a new prob that just started.