I've got a 10 year old Gerber toilet. Toilet Model # 21-552. Tank Model # 28-559, 10" rough in, 1.6gpf. It takes Flapper part # G0099647. I verified these numbers with Gerber customer care and a couple online parts places. Approx. 5 years ago I replaced the flappers on all three toilets in my house as they were starting to leak. I ordered the flapper part # listed above and the new ones I received worked great and stopped the leak. Recently I had to do this again as 2 of the 3 toilets in my house started leaking, where they would run to fill a slow leak in the tank. So I ordered 2 new flappers, same part number and put them on. They won't seal. The new ones leak worse then the old ones. Could my flush valve or fill valve be wore out and need replacing??? In other words it isn't the flapper but the flush valve? Thanks for your help.