'Phase transition point?' And you are asking ME??
Well, jeez, I am no polymer chemist, but was a biochemist, and this sounds to me like the well known petroleum based product attacking rubber or neoprene problem.
Send him a Tuf-Cloth with his buffer. Probably won't happen again. Of course, 15 years is a long time to expect a rubber part to last. I change the hoses and belts in my cars every 5 years or so, just because I realize the neoprene will not last forever.