I would be willing to bet that if you are basically shimming a worn cush, that the harder the rubber s Durometer (less compression) the better. Rubber sheet, the kind used for Vulcanizing worn industrial conveyor belting would be as good as you could find. If you can find a company that does this repair service, I would think, they would fix you up for free or at least dirt cheap, as there is a lot of shorts and scraps of various thickness sheets after every repair. I got a load of rubber from a outfit in Tacoma just for the asking, as it was going to recycle anyway.
