[AJbass]

First off, yes it was very likely over tightened. More than likely instead of using his or her 1/4 inch electric impact driver set on a low setting they used a larger impact driver not set on a low setting.
This is why you never use an impact driver for average bolt twisting work. Use a weak cordless drill to run them down, (if your too lazy to use the hand method) and a normal hand tool to tighten it.
Secondly, my normal gripe, they use junk materials to make things from. Never ever saw that on an old 50's and 60's vehicle, because they didn't go crazy with cast aluminum. Cheap material.
Constant use threads in all aluminum parts need to have hardened threads. So this is a manufacturing defect as well as a technician defect.
Can it be fixed? Yes, but you don't want metal chips entering the case. If it is tapped larger hope the metal chips are flushed out or removed by other means.

I was just going to say that! You have to be careful of, or flush out any metal debris that might fall into the casing if going the "tap out the hole" route. Good call, chidog!