Hi grumpy,
My research indicates that you can get room temperature cure 2-part pourable polyurehtane with a shore d hardness just under nylon (which I am assuming is the material used for the original part. Even allowing for the slightly softer material I expect the part to last long enough to justify the time/effort/money in making it and once the mold is done I can turn out a spare or two. Being slightly softer it may not be as brittle as the original and I will only have to deal with wear not breakage.
As for the metal gear, that is just 4mm mild steel plate I had lying around that I have cut by hand.
