See if he will split the cost with you of "sewing" the cracks with threaded, tapered plugs. It's a procedure that's been around at least since the 1940's, and it works.
Find the end of the crack, drill a hole, and thread it with a special tapered tap. Screw a cast iron plug into the hole, cut it off flush, and overlap the next threaded hole into the plug you just installed. Keep drilling, tapping, and installing plugs until you run out of crack. I've done it on many occasions, and the repair turns out leakproof, and usually compression-tight when used inside a combustion chamber. It will definitely seal a crack that has nothing but cooling system pressure against it.
Jerry
