Hmm, that is a concern. You said aftermarket, and by that you mean other than a B&S piston. Is the lock pin area differently designed than a briggs, meaning a steel wrist pin with 2 locks? Are you using new locks, or reusing old locks? Reason is steel and Mg don't like eachother too much. Can you post a pic of the failed piston, and all other components that have failed? You can't weld Mg. It will catch fire.