From your last description of the sight glass I would say that you have found your problem. I over filled my 02 the first time. That was before I found this group.
I did the same thing on my first oil change. A slight overfill, but first the breather must have been pulled out a little after the valve adjustment Found it! Then once installed, it puked oil into the air box. Once that stopped, the oil started leaking from the back side of the bevel gear housing. Maybe added oil increased pressure in the crankcase.
The best part of it all, I ended up going for the 7th gear option and it made bike more comfortable to ride.
All I need to do now is ride.