that's what i'm saying about the type of glass. different types of glass have different expansion coefficients and the sealants also have various expansion properties, and if you don't use materials that can withstand the temperature differentials, the sealants harden or gape, then you will get breaches in the surface.

also, i think the yellowing is probably not so much the glass as the type of polymer and its interaction with water. many kinds of polymers yellow with age and exposure, and consider the guarantee periods they specify on these things. they probably engineered it really tight to those periods so once it fails, a sufficient percentage of the time they were out of warranty and "does washing hands gesture" not our problem anymore.

this kind of thing is really common, you see it with semiconductor devices as well. as soon as the warranty is out a remarkable number of the devices fail.