So I have a typewriter with a diamond-hard platen. All the usual tricks for softening didn't work, and sanding the hard layer back revealed that the rubber had entirely perished all the way to the core; so I've removed it. Now, I'm in Australia, and there is no professional group here that replaces platens. So I've been looking at home fixes, old manufacturing techniques, and I think I have a solution. I have wrapped a few thin layers of cork around the platen core, and I intend to finish it off with perhaps two layers of heat shrink rubber tomorrow. I think the end result will be a platen with a firm strike face and a softer centre to absorb the strikes. My trial with the cork on its own was promising, but it was ultimately a little too soft. I could harden it with urethane or resin, but in the interest of being able to undo my work, I will try the rubber first. Will keep you informed.