I have changed the inside water control and the flapper three or four times, and the water still leaks out of the tank at a slow rate. I have also sanded around the opening in the tank, where the flapper sets, but the water still disappears. Looking for a solution. Thanks
Have you replaced the flush valve seat and riser for the overflow?
Sounds like you’ve eliminated the first suspects. The flush valve seat itself may be cracked or the riser tube for the overflow to the rim / bowl refill may be cracked.
I’m assuming the water disappears into the bowl, and is not leaking out onto the floor.