If there's no danger of hitting water, I'd stop-drill the end of the crack and install a threaded plug to keep it from spreading, then go ahead with the sleeve job. Of course, getting a close-up look is a much better method of evaluating the problem than listening to some keyboard commando (even me) from a couple of states away!
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!