Takes 2 hours of balls to the walls flying to seat the rings in a lycoming. Prior to that you'd never get anything on a compression test leak down. If I leave any airplane all winter without touching the prop(read turning the engine), there will be one cylinder that only reads 45 to 55 / 80 on a leak down due to the minor rust the open valves on that cylinder get over the Winter. Either stake the valve (read hit with a hammer) or run the engine and leak down will be 75 to 78/80 again. Can't see this situation being any different with an un-run car engine. Those rings don't seat themselves sitting in there...
