You may also be experiencing that the piston rings on this particular cylinder has seized. That you may have had slightly high CHT/EGT`s on the engine or maby this one cylinder. Even carbon build-up may have caused the rings to be slightly stuck, and once warmed up they loosend back to normal ?
But indeed, turning the prop the wrong way may drain your oil galleries and may cause a lifter to collapse. But on the other hand, that wouldent cause a low compression. This would only cause the valves to not fully open. They would still close just fine.
