Crane ( Ductile Iron ) rocker arms

The problem wasn’t underhardening, it was overhardening. The adjusters were brittle.

Maybe so but overhardening would cause the balls to snap. Underhardening (soft metal) which I've experienced causes premature wear thus metal shavings. Both were problems. Most all the problems stemmed from product produced offshore. Just because it says "Made In America" doesn't mean the individual components were. Best solution for the op, buy adjusters from Smith Brothers for piece of mind.