Look how the Oring fits into to the crank main seal lip recess. The Oring fills the empty space and prevents the main seal from inverting (turning inside out) when too much oil in the sump creates increased hydraulic pressure. This is really the only problem that can happen from wet sumping (other than increased kickstart resistance). There should be approx .020″ to zero clearance between the Oring and the engine (or belt drive) sprocket and this minimal clearance is what you want to prevent the main seal from inverting.
