I have a Universal/Rundle toilet, model # 4436, manufactured in 1965. I've replaced only the lift strap and the small disk on the underside of the tilt valve. Lately, the tank has been refilling every few hours when the level is about an inch under the water line. I've been told by my local hardware store that parts no longer exist for this model. I'm assuming that the valve assembly itself will need to be replaced and I should have a licensed plumber do this work. What replacement parts/models will work for this particular toilet and what needs to be done? I'm not able to replace the toilet just now. Thanks!