Name that oil leak

I have a oil leak that is fouling the plug in the #6(5?) cylinder... I don't think it's the valve guide as the plug is actually wet and not just glazed (Otherwise think I should be seeing black smoke).

Any guesses on where the leak is coming from?

There's an o-ring that seals off the spark plug area from the heads. Its possible that the o-ring has gone bad so oil is able to get into the spark plug area.