ORIGINAL: downunder
I've never owned a 4 stroke though so I'm guessing it's never hand started which makes that method of recognising worn rings impossible.
I hand start my four strokes, but you also have other leakage paths to deal with.
You could check the ring gap, but you'd have to know what it should be in the first place. OS seems to follow the common recommendations. The Magnums I've measured had large ring gaps new out of the box.