Well we have always just used heat. We have used our torch and heated up the casting so that the rust breaks loose. By heating all the way around the bottom not the rod but the cast iron it expands it. Then put a pair of vise grips on the top portion and it will just twist off but be sure to do it when it is hot not to let it cool off till it is out. It may start to get tighter as it cools and you may just have to heat it up again to get it out. This will prevent breakage of the rods there at the bottom.
