I'd be quite interested to understand why it is that some rubber parts seem to stand the test of time OK, while others go hard and others become sticky.
One of my occasional pastimes is restoring audio DAT decks, and when the pinch roller starts to go, the bit error rate creeps up until the rf signal becomes impossible to lock on to and decode properly. The odd thing is that, even though most of the machines I work on are from the mid '90s, a roller from one machine can be in much better condition than another, even when the mechanisms are identical.