Just change the flush valve. It is designed to do that. It has a weak spot for this reason. Done them before from not flushing the flush valve when winterizing, you cant forget to do that weather your using AF or air.
Its not hard to do and you can do it yourself.
Take it of and with you when getting the new one as there different ones. You will be surprised how many they have hanging on the wall. My guess is many people do this at least once.