If it's actually cast iron, find an oldtime welder who really knows what he's doing. I'll bet he fixes it with brass, not nickel rod. Cast iron welding requires preheating, post-heating, peening, and an extraordinary amount of luck to work right. The part usually stress-cracks right beside the weld unless you get it exactly right the first time. Brazing is much simpler, and just as strong, if not more so. if it's cast aluminum instead of cast iron, TIG welding works pretty well.
Jerry
