Ernest Christley wrote:
Is there a way to replace the rubber sheathing, or is the whole joint
toasted?

Have you thought of a patch for a bicycle inner tube? These bond to the
inner tube using rubber cement and normally use adhesive to hold them in
place while the cement dries. They also come in different sizes, and
you can cut them to fit with scissors too.

Don't forget to replace the grease inside the boot.