Mine started leaking on the left after a few thousand miles. The right side never leaked ???
I replaced it five times and got it to stop temporarily with a thin coating of three-bond per Mr. Roper's emailed instructions.
Each time I cleaned the area thoroughly with the spark plug in place and then speared the oring with a sharp angled dental pick. A smear of three-bond and the ring went right back into the groove. Spark plug still in place to keep unwanted debris out of the expensive bits.
I solved the problem permanently by selling my '09 and replacing it with an '07 this past Saturday. Pictures to follow.