There really isn't much that can be done more than 30 years after the vulcanite has been applied to the camera. Just like there aren't very good preservatives for vinyl in a car. Once it begins use and exposure to the elements, it just starts to slowly degrade. Vulcanite outgasses and that is where it gets stinky, like sulphur. Eventually, the bonds that hold it together as the hard yet flexible rubber covering break down and it starts to crumble.
Some have used lexol with some success. Some have used preservative for old tires which makes sense in theory.
Phil Forrest