Many times the problem with these heaters is at the terminal connections and not actually an open in the element. Have you opened it up and checked the element. Take the wire off the terminals and scrape the corrosion off the end of the wires before checking for continuity. You can buy ni-chrome wire if needed, but you have to figure out the resistance of the element - if i recall the ni-chrome wire is rated by resistance per foot. You have to do some calculating. I can measure the resistance of the element if needed.
crazydoug