Ditto on the stud and threadlocker, but I'd also suggest drilling and tapping the thread a little deeper, to hopefully get past the crack. Since the block is on the ragged edge of being junk, that kind of repair doesn't have many downsides, if any.
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!