Gearbox oil leak

[PiotrK100]

Another "experience". Trying to figure out why but reasonably is hard for me and the problem is as follows:
I change gear oil 80W90 and refil as stated in manual 0,85l. I drive like 50-60 km and now I see oil drops comming out of the hole beneah the clutch and gearbox. Brick was on the centarl stand in garage for 2 days and on the flor was like 30 drops of fresh gear oil, so looks like exactly that one I did change. What can happens? I did not overfill and earlier all was ok no leakagge at all. Looks like overfilling to me but if so, will it leak so much while standing?

[Scott_]

Don't think I'm trying to imply anything with this question, but::
Does the oil have the very distinct gear oil odor of sulfer? 

Did you happen to measure how much oil came out of the gear box when you drained it?

How full is the crankcase oil level. Anything above 3/4 (the center dot being 1/2) of the sight glass will be at a level equal/higher than the lip edge of the output shaft seal. This can result in oil leakage thru the clutch nut o-ring if the conditions are right(old cracked).

[PiotrK100]

Yes, oil that is leaking has specific gearbox smell and is new so it must be that one I pure in. Unfortnately I did not measure how much oil come out, just drain (looks like about 1L) and refill. Oil lever in crankcase is a little above half and remains unchanged thru sight glass for long. I did like 30 km today and all leackage stops, for now. Anyway, will dissable all engine parts in the winter and will change all zimmerings. But anyway that is interesting.