OK, the stuff we use for building reproduction wheels is made by "Smooth-on".
http://www.smooth-on...1206/index.html
We have 3 different compounds on the shelf, 326 (60 minute cure) and 327 (2 to 4 hour cure) and "Smooth Cast Onyx" (3 minute cure). (Cure times off the labels). The 327 and 326 need color added to them when mixing.
The stuff stays in resin form till it kicks, and doesnt go to a useable "putty" stage so for repairs you will have to build a dam around the bit you want to repair, and pour in the liquid, let it cure and then shape it to what you want.
The cured product is best shaped with files and samdpaper, its very easy to get the stuff too hot with power tools (even a buffer) and it will start to melt. After shaping, its sanded with finer and finer sand paper until it can be polished. (pretty much what you did with the original wheel). Small voids and pits repaired later are undetectable after polishing.
I've never actually done it, but I have seen it done a few times. We make wheels that have a cast aluminum core that is put into a mold and then the plastic goopy poured in to form the grip around the outside. The whole thing done under vacuum.
The guy that does it did warn me that the 3 minute stuff does go off quick, often while you are still mixing it up.
We have gallon cans on the shelf, but I see they offer a "Trial Size" that seems like it might be perfect for our (tractor) uses.
This isnt one of our wheels, but it is this is what we reproduce:
Hope this is of help.