I feel that on the install you have had a plug not seat maybe. There is no way that the gap caused that. Big mystery!All the connections were perfect. I checked and double checked them everytime I pulled them as that would have been an easy fix. What I'm wondering now is how would the gap have changed or if it didn't why did they work before since changing the gap fixed the problem?
On a second note. Whats wrong with putting antiseize on plug threads? If you have antiseize on the thread then you dont have to worry bout them breaking and dont have to use cleaner to get them out! And a lil antiseize goes a long ways. Your supposed to use antiseize on any aluminum threads or studs especially when heat and water is involved with it! I have used it on the threads and never had a problem and have never used any cleaner. Never had a miss or any fouled plugs and I check and change them often with N2O!