i have welded blocks did one that was open up about 10inch in the valley.that block that was worth $3000+ new so it was fixed .would be nice to fix it right before it is trash . you could try to pour some moroso 35500 or the all weather 35520 and run it till it get hot with out the spark plug in that hole that is leaking . then let cool try putting the plug back in and see if sealer plug the crack????