That crack needs to be drilled at either end and patched, or (and much better) - have it professionally welded. It's a small weld, so shouldn't be too expensive. As for the pitting - you need to be concerned about pinpoint holes. Unless it is a small enough area that you can put a patch over, the most practical option is to do a smear coat of JB weld over the area on the outside, to fill the pits, then Gluvit the area on the inside as extra insurance.
