My older Eljer toilet has a poor seal causing water to run pretty constantly into the bowl. A quick inspection shows the flapper ball stop sits directly on top of the porcelean -- there is no flush valve seat. I tried a couple different rubber gaskets and cannot seem to get a tight seal. Think I can get by with simply a rubber gasket with silicone sealant, or should I install a flush valve seat? If the latter, I cannot find valve seats at my local store. Everything I've come across for repair suggestions assumes the seat already exists. Not in my case...