Rubber probably doesn't shrink.  But as it ages, it first turns hard, then some years later cracks and in some cases turns very soft, like chewing gum.  Then the 'chewing gum' rubber hardens again and becomes very brittle.  This applies to all sorts of rubber - grommets, feet, rubber stops, feed rolls.  Platens tend just to go very hard but do not shrink until they are 100-plus years old.  Then they crack.