Ours went bad after a decade of use... Easy to replace, too, just make sure you get the correct flapper for your Toto. Most use the recent Korky OEM 2023BP/2021BP flapper.
OEM Korky 2021BP Flapper for most Toto toilets: https://amzn.to/3LYNZJs
#toiletrepair #howto #korky