My advice would be remove the drain screw drain off whatever oil is in the primary case then top up with fresh oil I have been using straight 20 grade fork oil in all my bikes for over 20 years now without any problems, the reason I was advised years ago to use fork oil is that it contains an anti emulsifying agent whereas engine oil does not. Also I do not go off level screws as they can be misleading depends on how level the ground is that the bike is standing on. I prefer to measure the exact amount of oil out much more accurate, and as a final point do not forget that you need to have a fibre washer on both the level and drain screws otherwise you will have a potential oil leak assuming your bike is swinging arm model then the correct amount of oil for your bike is 225cc or 0.4 pint.