Thanks boo. I just tried to find some exploded views of these assembly parts for better understanding. But failed for the GT300i.
Anyway, I understand the most of what you are explaining. If I understood you right, your scooter does have TWO breather hoses. ONe goes directly into the drivetrain to the clutch (which is indeed strange) and the other one into the airfilter housing. Right?
Fortunately my scooter (Like 200i) does have only ONE breather hose coming from the rear axle gearbox and going directly into the airfilter housing.
And that´s most probably right that way and a good thing, because I want this blow by fumes hose opening be protected from water and dirt. The best place to achieve this imho, might be the airfilter housing. Doesn´t it? Don´t want to have water and dirt/sand in my gearbox.
Of course there might be a problem with excess gear oil in there when overfilling the gearbox. Hence overfilling should never be done.
I always use(d) synth gear oil and never overfill(ed). And therefore never have and had the slightest problems, either with oilfoam , fume or excess oil itself. :-)
So, even if there was an overfilling going on and some oil came into the airfilter housing, it shouldn´t have a harmful effect on the drivetrain. In my case there is no connection from the gearbox to the drivetrain whatsoever.
The oil maybe could only drop down from the airfilter housing to the outside of the drivetrain housing doing no harm, except making a oily mess and dripping further to the ground. And the drivetrain housings should be connected via a rubber or paper gasket, so that no oil, water or dirt can get in there.
But I understand, that different vehicles might have different systems and solutions here, which I dont know yet and never have seen.