"...but all indications are that under normal usage, they should last forever..."
Hmmm. I wouldn't bet on that. These squishy plastics typically include plasticisers, which typically eventually leach to the surface and makes it sticky.
Think old polythene bags. Think old polythene tubing. And I have some decades-old, top-quality, agglomerated cork which has a most unpleasant (and probably carcinogenic) acrid taste one the surface now. No doubt some plasticiser. The jury's out as far as I am concerned, unless we get reliable guarantees specific to these sorts of problems, determined by appropriate testing. On the other hand, I have goldbeaters skin that is decades old, with no apparent deterioration.