I have a 1977 Mansfield one piece low boy toilet #11631 sold under Montgomery Ward name. It has an Indiana Brass 79 E fill valve. Not sure who makes the flush valve. It is brass with an angled seat and attaches from inside the tank. I use a Radiator specialty #264 flapper. After a few years the rubber gets a black film on it and has to be replaced. I replaced with a a spare Radiator flapper and it did not work. Went out and bought a new one thinking my spare had aged and it did not work. I steel wooled the brass lip of the flush valve thinking that it must have a nick or crud. No effect. Can't get flush valve out to inspect closer. I thought it could be rubber gasket under flush valve, but if it is the water stays in the tank until above the rubber gasket under the flush valve. But that seems like my only solution at this point. The problem is what flush valve replace it with ( Rember tank water depth is only 4 inches) ?
(This is an old house. When I bought the house it took me awhile to figure out only a Radiator specialty#264 would work. There is only one store I know that carries it. It has to very soft as there is not alot of water pressure to seal it. The flapper needs to float well because it's a low boy. The nose into the valve has to be short or it interferes with the valve. The reach has to be right because the valve has its own brass pegs that interfere with any other method of attaching. Replacing the toilet is also difficult. It needs to be under 22" tall and it has 14 inch rough in. )
(This is an old house. When I bought the house it took me awhile to figure out only a Radiator specialty#264 would work. There is only one store I know that carries it. It has to very soft as there is not alot of water pressure to seal it. The flapper needs to float well because it's a low boy. The nose into the valve has to be short or it interferes with the valve. The reach has to be right because the valve has its own brass pegs that interfere with any other method of attaching. Replacing the toilet is also difficult. It needs to be under 22" tall and it has 14 inch rough in. )