Due to iron and minerals in our well water (I have a filter at the well), the toilet fill valves develop leaks fairly soon after replacing the fill valve kits. I used to be able to buy just the plunger washers and they were cheap; now I can only find the repair kits for $5 or so, when only the washers need replacing. When they leak, I find bits of rust and mineral stuck to the washers and the washers have become deformed to the point that they still leak after removing the chunks. Short of installing point-of-use filters at each toilet (4 in the house), I can't see a way to keep the chunks from impacting the fill valves. Does anyone know of a source of the washers alone? They're 1B1 Master Mark IV valves. Alternatively, is there a type of fill valve that's not so succeptible to this kind of leakage, or that would have more economical individual repair parts?