Tear Aid A for urethane. I had the same question a few years ago and called Sotar directly. It also works on hypalon. I sold the Sotar, but still have it for my new(er) raft. Has not been field tested by me or anyone I know, sorry.
"Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." - Mark Twain