I've used ATF very successfully on engines with stuck rings. I had a cylinder jump from 70 psi to 220 psi. A good way to clean valves and combustion chambers and also fix stuck or siezed rings is to fill all cylinders with ATF so that it is coming out the spark plug hole. Let it sit for a couple of days. Suction out any ATF that is remaining in the cylinder. Do an oil change to remove the ATF that seeped past the rings and into the pan. Crank the motor over with the plugs out to remove as much liquid ATF from the cylinders. Start the motor up and watch out. It will smoke for over an hour sometimes especially if the ATF makes it into the exhaust. Cleans up real nice.