I fought this battle, as have MANY others. First off the 3/8 extention is not the right tool for the job. They really DO make a pipe plug remover (its like a really solid extention Without the detent ball, and made of hardend steel. I would recomend getting a REALLY good impact (3/4 or even bigger would be great) and try not to use any extention between the gun and the plug remover.

When all that fails, You can drill a hole through the plug, then use a hack saw blade to cut a few groves into the remaining portion of the plug--careful--don't go into the housing threads, and then tap the remaining portions of the plug into the centerpoint and they may come out.

When that doesn't work, take off the housing and heat up the are CHERRY red and remove.

Then use the opportunity to buy a new ALUMINUM housing from 440Source for about $70 (A bargain) and just replace the whole thing.