You can replace that flapper easily. They are sold at any hardware store, and even walmart. Look for one similar to the one you have.

Check your valve for adjustment please.

Sounds like the float is sticking. Could be a bit of rust or hard water deposits.

Thanks for the advice, guys. I think I've narrowed the problem down to the fill valve. Even when it is in the upright position, the water continues to run into the tank. Don't know why it eventually stops, but it appears that I will have to have it replaced. This toilet is fitted in a fairly tight spot between the vanity and the tub and I'm in my 70's, so it is difficult for me to crawl around on the floor to get it done, but it is such a simple operation, I hate to spend $150-$200 to have a plumber do it for me. Wish me luck.

It sounds like a faulty seal in the flush valve. Some, like the Fluidmaster, have replaceable seals.

• Fluidmaster400A Universal Toilet Fill Valve
• FluidmasterReplacement Toilet Fill Valve Seal for 400A Fill Valves
• FluidmasterUniversal Toilet Fill Valve and 2 in. Toilet Flapper Repair Kit

etc.