I broke a Mopar alum roller rocker (same as a Crane gold). Took a while to understand why, but it turned out that the ground electrode came off of the spark plug and momentarily created a solid "hit" on that valve rocker. Replaced that one rocker and still run them now, 2 years later with no problems.
In your case though, seeing where its damaged, I'm wondering if its possible that the jamb nut was over tightened, causing the inital weakening. Just an idea, but I do agree, you gotta find the root cause of the failure.

Brian