How to remove that permanently stuck toilet tank bolt!
After all else fails, try this first. Your regular handsaw. Whack the non-blade side about two dozen times with a file creating a jagged edge, Saw the opposite way into the clearance the tank has to its seat. I tried with just a hacksaw blade and days later still at it. This way the saw reverse trick is thick and quick. 20 seconds and goodbye stuck bolts! But as you know, be very careful with the blades on the opposite side.