What I have always done to check for a leak on the crank case was that I would spray contact cleaner on the crankcase and wipe off all dirt and oil. Then I would ride the old 'shee on the road up to a good hot temp and check all over to find the leak. It could be from anywhere. From the crankcase halves, to shaft seals, to the dipstick, to the clutch cover gasket. This may not answer your question but it is a good way to start looking for the leak.