Not sure about the Vaseline but both are a petroleum based product. I did the emergency brake cable boot off my scout and it's like new? Supple, soft, and pliable. I think rubber has a lot of silicone in it and it's the silicone evaporates from the rubber; which, makes the rubber brittle. The rubber acts like a sponge and absorbs the silicone. I put one of them red straws on the can of silicone; then, put the parts in zip lock bag and closed it with straw in bag and sprayed. Not near has many fume's.