I have a couple of Kohler Wellworth toilets. Both of them are about 3 years old, and both have had the same problem. The flapper valve does not consistently close well...consequently, the tank drains and must refill. I have tried the typical: 1) Cleaned the valve and where it seats on the toilet. 2) Lightly sanded the surface where it seats. 3) Replaced the valve. They are OK for a while, but then I have to go through the same routine again in less than a year. I don't ever remember replacing flapper valves that soon. - We have fairly hard water. - I have used the types of flapper valves that are supposed to be resistant to the chemicals in the water (should I switch to the regular rubber ones?). - I also have a suspicion that maybe the valves collect small air bubbles...and become too buoyant. Again, maybe a slightly different material composition for the valve would combat that. Any suggestions or troubleshooting tips? Thanks in advance. Bob