started the check for bad plugs by pulling the spark plug wires one by one. Got to #4 cylinder and it was definitely not firing. all 4 contacts on the spark plug wires were firing (tested them with the end of a screwdriver). There was a fair amount of oil in the #4 spark plug recess, leaving about 1/4" worth of residue inside the socket. Is this an indication of wear in the valve cover gasket, head gasket, or possibly both? It's on old car with lots of miles so i wouldn't be surprised at either. I've not seen any oil in the radiator fluid or white smoke in the exhaust which I understand are common indications of head gasket failure. The leak on the valve cover gasket is worst near the #4 cylinder. I intend to replace it next week. I found a video of it being done on this exact vehicle and it looks pretty straightforward.

I've got some new plugs i'm about to gap em and change em. I'll give an update on whether it fixes it or not.