Norbert. The early design of engine does not have an oilseal on the crankshaft. Instead there is just a large washer, we call this an oil slinger, so not a perfect seal as mentioned in my earlier post. For now I would set the oil level in the chaincase as normal, use the bike and see how much oil is being lost from the chaincase. We assume it is not simply leaking out. Make sure there really is a problem, not just things settling down after the rebuild. Use a simple wire dipstick and check the level on the cold engine after standing, preferably overnight.
If there proves to be something wrong and oil is actually leaving the chaincase, the most likely cause is that the slinger washer (Described as a Bearing Shim) is missing, the drive sleeve is the wrong one or the crankcase is damaged. To inspect this the cush drive and drive sprocket need to be removed. The drive sleeve should match the crankcase very closely, and with the drive sleeve pulled from the crank, you should see the washer, not the ball bearing. Your video had lots of crankcase oil fumes from the chaincase, so there is an obvious connection somehow between the crankcase and chaincase.
The oil level setting on later models was lowered to help prevent oil getting into the clutch. The chaincase cover simply has the cut out to set the level moved to a lower retaining bolt position as shown in published data.
Swarfy.