The name of the stuff for conditioning rubber is made by a company called
adamspolishes.com - VRT vinyl, rubber & tire protectant. What I did was I bought some used stamps that were very old and very hard as a rock brittle rubber so, I put the stamp on a lid to a old coffee can and dabbed with a shop rag the vrt onto the rubber and let it sit, and it absorbed part of it, I ended up doing this 3 or 4 times and then I was able to push my finger into the rubber and have some give to it again. I did it in the garage so, I don't know if I remember how many fumes it had.