LeeAnna, you might check to see if the crack or something else is the problem. One way to do this is to put some food color in the tank and watch to see where and how the color works its way to the bowl.
One other thing that might be happening is that the flatter valve is not sealing into its hole. This is not uncommon because mineral build-up can occur in the area where the flapper fits into its seat. A good cleaning of this area with CLR or similar calcium, lime, rust removers might be in order. Be sure you follow the label instructions for the remover.