Thanks ShadowCory. The idea to cast miniature tank tracks from a mold is not mine, you can find some examples here:
Making Tracks: Casting Tread Plates for my Rebel Grots
https://creativetwilight.com/making-...-tread-plates/
True Scale Rhinos, Predators, Vindicators, and oh yes...Land
True Scale Rhinos, Predators, Vindicators, and oh yes...Land - + WORKS IN PROGRESS + - The Bolter and Chainsword
As for the silicone mix: I've only tried silicone + lighter fluid, and silicone + soapy water.
As far as I know, silicone + corn starch works well too, but it does result in a stiffer mold, and since I'm casting with fairly fragile material, I wanted the mold to give a bit more.