Re:
When you say sheared, do you mean the bolt has snapped in the hole or that the bolt has stripped the threads in the clamp?
If its the clamp threads that have stripped, have you tried using a longer bolt? The XT bolt is notoriously short while the threads in the clamp are very long - means that there are still good threads in the clamp. Old shop trick is to swap the longer bolt holding the shifter to the clamp with the shorter bar clamp bolt