The fact that these seem to crumble right where the O-ring is sure has me wondering. Plastic should be OK for quite awhile, but apart from the seams in the originals occasionally rupturing, the failure point seems to be the base. Yes, the plastic is probably thinner there, but I wonder if something about the coolant and the rubber O-ring is leaching plasticizers out of the plastic or something, leading to the deterioration.
Moot point, I suppose.
Moot point, I suppose.