I have a (25 yr old) one-piece Am Standard toilet (3.5 gal flush). Flush valve actuator looks like 2 tubes perpendicular to each other with a disc that covers the hole in the tank. Have replaced the actuator and disc twice and the brass ring seat & washer once, all with Am Standard parts. Still it leaks (did dye test). Situation especially annoying, not to mention wasteful, because a plumber replaced the original (leaky) ballcock with a fluidmaster that treats us to a phantom flush (3 times/hr) when water level goes down 1 inch (it also doesn't fit in the tank properly to allow the tank to fill to appropriate level because of the low profile of the entire toilet), but alas, that's a separate issue. Don't see this type of actuator/flapper problem addressed anywhere in repair info/books. Am at a loss; is there:(1)a design flaw with this type of flush valve (2)a solution here (3)or do I just need to get a new toilet?