Here is the problem. Today, my toilet tank filled up slowly if at all. I looked in the tank and the water is flowing into the overflow tube and at a good rate, but the level changes very little for the amount of water going into the tank. I checked the flapper valve and it appears to seated, in fact I know it is. If I now take the hose going into the overflow tube and let it go into the tank directly, it fills up properly, the water shuts off when the tank is full, and the water stays in the tank with out leaking. I read on a site that the overflow tube assembly is probably at fault and needs replaced. Correct? Are there standard replacement parts or do I need to take the parts with me?