Does anyone know where I could send a head for a Fox 15 for re-threading? This engine's pushing 45 years old and I'm trying to reserect it, but after close examination I discovered the threads for the glow plug have been somewhat stripped at one time therefore not allowing a compression tight seal. My local machine shop insists there aren't helicoils in 1/4-36, so I'm at a loss. I've since checked with Fox, and they can't do it either. Any help would be appreciated. Thanks