I've run out of ideas and need some plumber's opinions. I have a one-piece American Standard toilet (new style #5, if that helps) on which I recently replaced the whole old ballcock/fill valve assembly with a Fluidmaster 400A. That went in fine, no problem. I also bought a replacement (non-AS parts) Acutator and disk becuase, like a genius, I accidentally snapped the old one off its base before I realized how it's attached. Okay, new Actuator (the tube flapper) and new disk that comes with it go in. After the fill valve stops, there's still a contant (although small) amount of water running into the bowl. I turn the water off, watch it slowly run down to the bottom of the tank, and suppose it's the gasket between the Acutoator base and the bottom of the tank. I bought a replacment AS gasket and installed it. No difference, even though I tightened it well. I took new disk 1 off of the Actuator and replaced it with new disk 2 (from Fluidmaster) and it still leaks, but a whole lot less. Still, the water level eventually gets low enough to trip the valve for a second or two. Also, when flushing, sometimes the Actuator doesn't close over the hole fast enough, so it actaully bounces up and down and eveything continues to run. *Sigh*. The only thing not yet replaced is the whole Actuator assembly (float,disk and base) with true American Standard parts. The plumbing supply place keeps unkind hours, meaning I'm looking at another week, but before I go back again I was wondering if this make sense to anybody. Do one set of replacement parts *REALLY* make that much of a difference? Or does this leak sound like (God forbid) a crack in the tank or some other bigger problem? I can't believe that this is giving me this mich grief, I've done this on other toliets before with success. Any help greatly appreciated.