Inner axles that twist and snap can be from overpower and abuse, common enough. It can also be from cheap imported axles sold for the past 20+ years. Rebuilt axles today have issues, new axles have issues. If you broke an axle you most likely need to address the internals of the diff as well to strengthen them. This is not usually what you will find from a vette vendor or local shop. Since I don't know the shops in your area I can't say for sure but having been building these for many years and having my own Corvette Machine Shop I know how things have been done and again the past 20 years a lot has changed. Be very cautious of some of the websites out there promoting Bulletproof or Race differentials. You need to know exactly what any diff is built with and the procedures used. There are some very good conmen out there that will tell you everything you want to hear, take your money, and then disappear or ship you junk. Word of advice, stay away from some of the Southern vendors.