Have a close look at the shifter seal.
+1.
1-Take the side cover off. (will need to remove the shifter to do so)
2-Completely clean that area.
3-De-grease entire underside of engine as well.
4-Go ride.
5-When you see the leak again, go back to step one.
6-Find leak.
There are a few different o-rings under that cover.
Most likely is the shift shaft seal. Then maybe oil pressure sender. Or oil galley relief plug(s).
Worse case scenario is the case seal, behind the front sprocket. Doesn't usually leak though.
Let us know what you find.