Ditto on the F plug. I tried several and the F plug was the only plug that actually kept the engine from cutting off at idle. I still have my little evo1.00nx in the closet...was on my desk earlier this year as a paper weight over accounts payable stack. I'll check on O ring when I get a chance. If it was missing, it sure didn't help matters any. That would explain the overheating seizures if it was drawing more air than needed and running lean.