Sheldon Brown calls the glue in patch kits "rubber cement" and who am I to argue with that. I think the actual vulcanizing agent is what applied to the patch. It works with the rubber cement to form a bond with the tube. Unvulcanized natural rubber (from rubber trees) is much more reactive than the vulcanized butyl rubber in the tube and whatever is in the patch. If the rubber in rubber cement is natural rubber, it is all set to react with vulcanizing agents and then with the patch and the tube. If it is in contact with both the tube and the patch while that reaction is taking place, then it would attach to both sides and make a bridge between the patch and the tube. I actually think this is what is going on. In a word NO, your Dural is not likely the right stuff. Bulk packaged rubber cement could be just fine though.