Thank you all for your suggestions, I have a steep learning curve ahead, bought the bike 3 days ago. :-)
I will start with the ATF, if the oil comes from the primary would that mean that the gear box seal might be OK and it¨s the felt washer thats faulty? (Might be a stupid question...)
Can also mention that I might have overfilled the primary after finding it empty, filled it up to the lower screw level on the primary outer cover.
Edit: Forgot one important thing, when it was empty there were no leaks suggesting it is the primary oil that's leaking.
I am used to and spoiled by the relative simplicity of electric motorcycles, more or less 3 parts, motor, controller and batteries, so more or less advanced mechanics requires a different way of thinking. ;-)
Heres a pic of the bike, not completely original as you can see: