Had same problem
Lost plug, it fell down into the bowels of the engine..... Replacement available as part of HPOP, was told.. So, used a bolt... Ground hex off head, making it round for clearance issues... Cut screwdriver slot in top w/hacksaw.. THEN went to find a 'gasket' that would hold the pressure..
After several tries, including O-rings, copper, etc..found a nylon washer of correct size, and that seems to be holding OK..
good luck..
Lost plug, it fell down into the bowels of the engine..... Replacement available as part of HPOP, was told.. So, used a bolt... Ground hex off head, making it round for clearance issues... Cut screwdriver slot in top w/hacksaw.. THEN went to find a 'gasket' that would hold the pressure..
After several tries, including O-rings, copper, etc..found a nylon washer of correct size, and that seems to be holding OK..
good luck..