After you flush, use the top of your foot to push the pedal back up. It should stop the water flow.
The problem with the Aqua-Magic Style II Toilet
is poor design. Even if you replace the valve, or purchase the exact same new toilet, it will eventually happen again.
Hard water eventually causes the gasket to not slide as easily on the valve ball. The weak spring used in the valve cannot overcome the drag, so the valve stays a tiny bit, (or alot), open.
Whatever you do, don't leave the coach with the flush valve on. it will flood.