I had some of the same issues. I took the toilet apart and cleaned the gasket but it did not last. I finally bought the parts and replaced them, all is well now. There was so much crud built up around the ball it did not have a chance to work correctly.
Replacing the ball was not that easy for me. I am sure that there is a secret to it. I ended up putting a screw into the old one to get it out of the toilet. Then, I put electrical tape around the new one to avoid dropping it into the tank. Good luck.
2007 Fleetwood Bounder 38V