It is not a carb. vent or overflow is it?
In fact ... I don't know ...
I really noticed the leak last week-end by a tiny oily spot on the garage floor.
impossible then to know where it was coming from.
but I could see that the gear box was oily and the spot was under the filling bolt (but obviously not coming from there)
When you say its leaking from the transmission, where is the puddle? under the center stand or under the rear wheel hub? Remember, the only transmission with oil in it is in the rear wheel hub. You did not specify where the leak is.
Next ride (a longer one this time ... about 1 hour / 30km)
I checked carefully when I stop the engine and put the scooter on the centerstand.
that's where I noticed that the oil seems to come from behind the air filter box...
could see a couple of droplets falling from that area.... run on the silver transmission gear down to the floor.
I then noticed a hose filled with pink oil (smells and really look like gear oil ... my old father thinks the same thing)
it's one of the hoses going being the black filter box ...
Those are my observations for now ...
I will surely verify next week-end the quantity of oil in the transmission gear (perhaps too much oil was put before delivering the scooter to me)
I will try to open the filling bolt when the scooter is at rest for 2-3 min. after the ride .... see if oil is overflowing by there
and ... contact the dealer to explain and have his opinion ...