For best operation, you have three choices: replace the existing valve which is non-repairable; buy the Toto version of the Korky valve; buy the ADJUSTABLE version of the generic Korky valve. The non-adjustable Korky (they all adjust in height, but not in the water distribution) won't fill the tank and bowl properly. The adjustable one takes a few flushes to get the balance between the tank and bowl proper. The one made for Korky has that adjustment made for you. The valve senses the tank water level. If the bowl isn't filled up by the time that happens, it won't flush properly. If it overfills the bowl, it wastes water. That's why you need one that can make the balance between the bowl and tank so they both fill to capacity at the same time.