2002 Gt - Oil On Electrode

Do a compression test on that cylinder. Could be bad rings...?

^^^Id start with a compression test if thats good then most likely just a valve seal. Bad valve seals tend to just smoke a lot as oil drips into the chamber and rarely is it bad enough to fail a good plug out. A valve seal would pretty much have to be completely gone to fail a plug that fast and would smoke like a freight train. Bad rings also tend to smoke and compression wouldn't come and go as you stated... It could also be a combo of a bad valve seal and a burnt valve?

Oddly if you don't have a compression tester there's a old skool trick that involves poring a little bit of oil into the chamber to test for rings and burnt valves the idea is you poor a little bit of oil in and the oil will temporarily seal up the rings for a short time...

Anyway
You should also look into the reason why it did this a clogged cat could easily cook valve seals/valves/rings and would also hide some of the smoke