How much above the top of your extension is this can located.
I've seen a few masts break where a tall extension was used and the lowest
cam and the top of the extension were about the same height from the bottom of the mast.
The mast then gets "point loaded" on both the inside (the top of the mast base) and the outside (the cam).
The Sting was a 50-75% Mast, right?
Was there a groove in the mast where the misaligned cam was rubbing?
Hope this helps,