I like to tinker. Tore it down to investigate. The piston ring is surely stuck due to carbon. Cylinder and piston are free of any scoring.Cleaned the ring lands with a razor blade and its soaking for the time being. I am not investing anything into it. There's no way to remove the ring without breaking it. If it doesn't get freed up, it's tossed.What kind of compression tester was it? If the tester's one-way valve is not at the tip of the line that's attached to the plug hole, you'll likely pull a false lower reading. I have a cheap tester that won't work because it requires a thread adapter which adds more volume to the displacement.