I have seen that Wilton model broken before. The old school fix for that would be to clean up the parts, bevel the crack out, pre-heat up the material, and the vice. Use nickle rod fill, and clean, fill and clean, fill and clean, post heat with a torch, let the vice cool slowly. The old guys used to bury the hot project in sand, and let it cool very slowly. Wraping it up in heat blankets would also work. I have also used the torch, and heat it less and less over the course of a few hours.
One the other hand, I just bought a vise like that at a yard sale for 5 bucks. It needs a little help, but it is not broken.