After reading many posts re: how to fix / replace fill valves of Kohler one piece toilets, I decided to try cescobrass replacement fill valves. Ordered them online, received within 10 days and installed them in 30 minutes flat. I am a novice at minor repair and a plumber quoted me $100 labor and $100 replacement Kohler fill valve. Cescobrass 16AK cost me $61 and 30 minutes of my time! The part is solid and replacement is easy. Instructions are clear.
It might have been cheaper to buy various repair kits and try to repair the topcap of the fill valve but with 5 year warranty, I prefer the Scovill Model 16AK Ballcock for Kohler Toilets from CescoBrass. Just a satisfied customer!