While I don't have first hand experience with the 3.3, on most nitro engines the cooling head and the actual engine head where the plug threads in are two seperate pieces. It's possible that you stripped the engine head, how tight did you tighten the glow plug? I usually just spin my plug wrench down finger tight, then just snug the plug maybe 1/16 of a turn or so. Remember you are threading into aluminum so it's soft and easy to over do it.