I replaced an old Toto TSU08a.6 fill valve in a Drake toilet with a Korky 528MP. The installation was straightforward, but the fill level in the tank is not consistent. Most of the time it is just 1/4 to 1/2 inch below the top of the overflow tube, but about 1 time out of 4 it will be 1-2 inches below that level. Also, on those occasions, I could see a very slight dripping from the float portion of the valve into the tank. Do I have a faulty valve, or is there something I can do to remedy this?