the case has a drain screw
it also has a "fill to level" screw , either at about 5 oclock behind the clutch ... or
at about 7 oclock under the front sprocket .
if these are open , it allows oil over about 200 cc to drain out .
the idea being only the bottom of the chain needs to dip into oil .
...and too much oil will add drag over what is necessary to keep the chain oiled
8 oclock fill screw
5 oclock fill screw