Go to your hardware store, home center, walmart, etc and buy new ballcocks (water inlet valves) that have the float on the column and at the same time replace the flappers. Fluidmaster makes a good brand that many plumbers also use. They get old, corroded, worn out, etc. and aren't made to last forever. If fact (like in your case), when one starts to go bad, then they should be replaced for every toilet in the house. Then you are good for another 10 or more years.