Poly-urethane from McMaster Carr. About a 80 or 90 durometer. you can also buy casting urethane from McMaster Carr in 88 durometer. It is a 2-part urethane. I have used it to re-cast rubber parts as well as make new parts. I have made bushings new again by removing all the rubber and re-casting with urethane. Urethane is impervious to almost every chemical
It would work great for building transmission mounts if you cast it right.
