If it is the stabilizer in the rubber breaking down and rotting, get some foot powder and rub it into the rubber, brush off the excess, reapply, and do that until it stops being sticky. The rubber will suck up the powder and bind to that instead. As a consequence the more the stabilizer leeches out the more brittle the rubber becomes and it will begin splitting apart. Sadly nothing can be done to fix this other than if the factory would have used a quality manufacturing process. I have cell phones from the late 90s and early 2000's with the same problem.