Have you got shorter dog bones to raise the rear? This puts a lot more strain on the roller, as does a larger rear sprocket?

There was a thread a while back about mashed up lower rollers, but I don't recall broken brackets. However, it does give some insight into possible mods to prevent it happening in the future.

http://www.xt660.com/showthread.php?t=7646

For now though, I guess you'll have to get a bracket made up and welded in place, which is a bit of a ball ache, but do-able.

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