As said before, photo would be a great help.. Cracks, many times can be "repaired" with a wicking sealant from Loctite that's called "290." It's a thin liquid that soaks into cracks and since it's an anaerobic (cures in the absence of air) the compound it will only cure/seal once it soaks into the crack. How well it works depends on where the crack is. Usually works very well in threaded holes, sometimes works with cracks in freeze plug holes.