I just had the flapper valve fail one of my home's toilets. The rubber had become spongy, sticky, and was beginning to disintegrate. It's so soft now that it rubs off with the slightest touch.
The valve was installed by the previous homeowner, so I don't know its history. However, since I've moved in, this toilet has been very seldom used. It's in the "guest" bathroom, and unfortunately have guests over now who are inconvenienced.
I'd like to understand what happened here, so I can avoid something like this happening again.
Best Answer
Flapper valves in my bathrooms typically last about 2 1/2 years of so. Depending upon the type of material they either get mushy like the ones that you show or they start to get hard and no longer make a good seal. Since I do not add anything to the toilet water tank like a disinfectant or fragrant additive I have to attribute the degradation of the flappers to the water chemistry and the chlorine that the city adds to the water.
Flapper valves are relatively inexpensive and the type you show in your pictures only take a few minutes to replace.