The most common cause of a broken ear on a bellhousing, trans case, etc. is trying to bolt things together with a piece of debris trapped between mating parts. All it takes is a few thousandths' gap that can't close up for a brittle casting to break.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!