Do check to make sure the valve covers or crankcase breather tubes are not leaking. The first step of checking for an oil leak is to clean everything thoroughly and see where oil first appears. It is possible to add a fluorescent dye to the oil which shows up under ultraviolet light to better see where the leak originates. Besides the magneto rotor spinning and flinging, there is a segment in each rotation where both pistons are going down at the same time which will add pressure that is not fully mitigated by the crankcase breather tubes.