I have a set of of them and mine are still firm and don't show an signs of turning into gel. Makes me wonder if they were stored near isopropyl alcohol, MKP, acetone, or one of those other old style solvents and the VOC's ate them.
I've had very mixed responses from JessEm. If they do respond, ask what they are made of. At least that way you can do a material compatibility search and see if they were exposed to some type of solvent.