Toilet "Refilling" Every Few Hours
 

Recently, my Kohler Wellworth toilet, which is about 10 years old, began
refilling briefly every few hours. I replaced the original flapper with a
Fluidmaster 501 and the same thing happened the next day. A second new flapper was installed and, again, the toilet refills periodically. The problem may not be the flapper, I guess, but what else could it be? I did clean the seat where the flapper is supposed to seal, but nothing changed. Can anyone suggest what else I can try?

Are you sure it is leaking at the flapper valve?? If yes, the seat could be cracked. Check the tank bolts for indications of leakage, but that would leave water on the floor. Is the fill tube in top of the overflow below the water level?? If yes, could be siphoning, raise the tube.

to check for leak's in the stool. Put cake dye in the tank above so to color the water. Now if it is getting colored down in the stool than flapper. But 2 i doubt it is the flapper. a crack in the stand pipe or gasket bad. Depend's their could be a crack and letting water down the hole in the stool and not around the outside letting water down the outside ?? No other place for water to go

Pull the small hose out of the overflow, Tell us if it stops

No External Leak, What's That About The Flapper Seat?
 

There definitely no leak at the bolts which hold the tank to the toilet, but what about the ring where the flapper is supposed to make a seal? In this toilet that seat is a plastic ring. As you said, if that was cracked it would not allow the flapper to seal against it. Is that part replaceable? If so, do they sell them at Lowes Home Depot? I had never heard of that part going bad before. All my previous toilets had a built-in ceramic ring that was molded in a part of the tank. Thanks for the possible source of the leak.
I intend to try the dye-leak test, as has been suggested here, too.

Tested and Found It Does Leak
 

Not having any food coloring in the house I used four heaping teaspoons of instant coffee in one-half cup of water. After it was dissolved I poured it into the take and waited about 20 or 30 minutes. Sure enough, dark
color started appearing at the bottom of the bowl, getting darker every few minutes. That convinced me of what you folks told me, that water
was leaking from the tank to the bowl.

But, does it have to be the flapper? There is no siphoning going on because the small hose rises well above the water level, its end is also well above that level, too. Could it be anything else but the flapper? Someone mentioned a possible crack in the verticle tube, but I checked and it looks ok.

I have actually had one toilet that when i replaced the flapper, i noticed that the ring the flappers sits down on to seal up, was too big for the flapper and the flapper just barely covered it (i mean barely) you could take your finger and push the flapper down inside of the opening, so it continued to leak around the edge. I guess the original part had been changed out at some point. I'm not a plumber, but i swear i never knew there was more than one size. live and learn.

Alot of those kohler commodes take a special flapper, you can not use a generic fluidmaster one. and there are several different styles of special kohler flappers. Engineering genius not

like that was mentioned kohler commodes take a special flapper . 501 i belive you said you used. That is the most common one. I used to work at HD and sold lot's of them but if you can get some smart one at the Box's store that know's they can get you the right one. If not go to a plumbing store that just sell's kohler flapper's . The stand pipe can be replaced if that is the problum? I guess it is like replaceing everthing in the tank? Which is not the way to go than you will not know which part was defective? Flapper is the easyest to change. The stand pipe you have to take the tank off like the tank bolts lot's of work if not need to be. good luck