Jon Goodman used to sell some foam kits of the brand SEKISUI at some point. Are his kits still made with that foam brand ?
I have found out, that this peculiar brand foam will disintegrate into black goo sooner or later. On the other hand, the similar foam sheets of the brand NITTO sold by Aki Asahi from Japan hold very well over time (same storage condition, bought at the same time around 2005).
@Mauro : the best solution to fix a camera in need of new light seals is to buy a new mousepad off your local computer store, then cut some 2 mm square strips off its black foam backside with a blade. For most cameras you don't even have to use some glue, the new strips will hold in place by themselves in the camera back grooves. In case you need to glue them (or to glue a mirror damper sheet which you will custom cut shorter, thicker and wider, of course), a bit of casual houseware neoprene glue will do it. With one mousepad you can approx. fix a dozen of cameras. Auguri ! 😉