If you've never done a thing to the toilet over the years, I'd go to
Home Depot
and get one of their Fluidmaster kits that contain everything you need to
rebuild the whole
innards. Kit contains new flush valve, flapper valve, gaskets, tank bolts
and handle. While
you're in there might as well do the whole show for about $17.00. Assuming
you're tank
bolts aren't rusted to death, the whole deal might take an hour.