Solving a toilet tank leak

I never used an actual timer but 'about' every 3-4 hours the water would run to refill the toilet tank... I took the top off the tank and the water was going down about an inch and the automatic valve would then let water in to refill the tank
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I did the first, obvious thing and bought a new flapper valve... did not fix the problem
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So I did the next thing and removed the flapper valve assembly (see picture 1)
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The outside of a toilet tank is shiny/smooth due to being dipped in a 'slurry' before going into a kiln, but the inside of the tank is NOT smooth, so the rubber gasket at the base of the assembly was clearly not making a good seal (note ridges in the rubber gasket)
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My solution (see picture 2) was to use shop towels to get everything completely dry and put a thick bead of silicone caulk on the rubber gasket... reinstall and let 'cure' for 24 hours before opening the water valve to let the tank fill
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So far (2 days) the tank is staying full... leak is fixed !!!