Hi Dan.....I have had a simular incident and these guys may be able to solve your problem.
http://www.muggyweld.com/potmetal.html
They have videos you can see how the process is to repair pot metal and other diecast items. You have to buy their rods and flux but you can use a propane torch if you do not have a welder. Their rods can be used to fill pits in pot metal also. Hope this helps. Kim