A very interesting topic. We all have some very old bikes with rubber to match. Some good feedback on how the various treatments perform would be handy.
I have one bike with knee rubbers with no apparent means to attach or remove. I eventually found two slots cut in the rubber which allowed me to insert a small screwdriver. I used soapy water as lubricant, but it distorted the rubber though, and a good treatment may have minimised damage.
Col