Okay, nevermind then, don't put in that o-ring. Give your junk a bath in gasoline then come back on here and tell us that it burns like fire. Then we can all say I told you so. It'll be fun, trust me.
Really bro, all puns aside. You are playing with fire if you don't have something installed in your gas cap that will seal.
Hey, maybe I can market a gas cap that no o-ring will fit in. I think I'll call it Insta-Flame. Yeah...I'll market it as a training tool,"Guaranteed to keep your ass off the seat"!