My first thought is to try to seal it using thinned paint, or a cynoacrylite (?) glue that will work in with capilliary action. Worry that this will just fracture again and leave me with the same problem, so I am considering using a flowable windshield silicone -Permatex #65AR which is intended for flowing into windshield air leaks. Downside to silicone is if it dosn't work, nothing will want to stick to it afterwards. The next option is to go with a bead of polyurethane sealant on the outside surface, but this is the worst option cosmetically.
Any thoughts? TIA F. Plant