Using a sealant to stop a toilet tank leak
You can cut the bolts off with a mini hacksaw. The rubber washers inside the tank are shot, and that's what's causing your leak. You can fix it for $10.


Turn off water (I think you're already here).
Flush and sop up the remaining water in the tank with a sponge (or use a shop vac if you have one). 
Cut off the bolts and remove them.
Replace with new bolts and washers.
Refill tank and check for leaks.


Mini hacksaw: https://www.harborfreight.com/6-inch-mini-hacksaw-65341.html

Tank bolts: https://www.lowes.com/pd/Keeney-2-Pack-Bolts/1001094052