Was the plug loose in the head when you removed it? The "oil" could have come from the combustion chamber but if it was a lot of motor oil, then you a ring may be leaking which is a bigger problem.

When you say #4 cyl, how are you counting them? I've seen the plug wells filled with detail liquid on a buddies which caused it to misfire badly - but the engine sure shined!

What did the plugs look like that you took out? That is probably the biggest help in troubleshooting misfires. Are you using premium fuel?

If you have a 00-01 VX, the computer will often throw codes if using the Bosch+4s (and probably others). What plugs are you using and what did you gap them at?