I fixed ours by just replacing it with a Thetford "Style II" works great now and not much hassle and messing around. Glad I got rid of the original no count loser stool.... :) Replacement cost no big deal and now warranty in force. Cost around $156 online.
OnEdit: I will admit that they all seem to suffer from certain water supply problems. Ours doesn't like the high calcium content in the Rio Grande Valley water. The Thetford however is easier to change the seal if needed and the ball seems to work well all the time unless calcium buildup occurs. (about every 1.5 to 2 years of use for us.)