I don't know what the problem is with this valve, but if it was mine, I'd replace it with a new 1/4 turn valve. They are far superior to the old many-twist type. Toilet supply valves should always be full on, so there is no advantage whatsoever to having to make several turns on the valve. The 1/4 turn style are much easier to turn off when necessary also. They come in every connection configuration, so fitting will be no problem.