This is the second time it has happened and both times its been on the left cylinder. I do know how to correctly install the o-rings. I use plenty of grease to keep them seated . I also torque to the correct specs. in proper order and don't over tighten. My set up is 4 mill mx port . Domes cut by same guy who did port job . Site sponsor here. Chariot head 21 cc domes running a 50/50 mix. Jetting is a tad rich but very close. No signs of deto. The viton o-ring on the left cylinder will get a thinspot in it and allow water into the cylinder this has happened twice since I have had these higher compression domes. Prob bout six months apart. I'm gonna try it one more time then if it does it again I know I def got a prob somewhere. Any suggestions on where to look Possible things that may be causing this ?