[M.A.C]

I would try to seal it with one of the many products that can seal head gasket leaks. Why not? Just follow product instructions to the letter as some, if not all of the head gasket sealers, require the radiator to be flushed. If sealer is left in without flushing it could clog the radiator. I've used Solder Seal/Block Seal to repair a severe head gasket leak and it worked. But I wasn't dealing with a Northstar engine so I wouldn't know if it will work for you. If it doesn't work, then you can always reconsider the other options.