Toto Toilet Problem

Hi guys,
Bought a Toto Eco Supreme in August and have had this problem twice. The tank is losing water. I hear the valve leaking drops of water, but the tank is half full of water. The bowl has the same amount of water it had after a flush. The valve has a number 26 on it. Any ideas? No water is on outside of the toilet.

Ez

Most likely the flapper is not closing tightly.

I've tried adjusting the chain and lever, but it still leaks. It doesn't happen right away, but a few hours later, we hear the toilet running and a hissing sound from the fill valve when the water gets low in the tank. Can't really tell if the flapper is seated right or not. I guess I'll call Toto for a replacement flapper.