The LH carb collects oil on the bottom of it when you park the bike on the sidestand. Ends up running down inside he tube and leaking out between the plastic tub and the metal carb intake.
This may be crazy but I have turned the tube arround on mine so that the rubber hose is between the plastic air tube and the carb. This seals the connection better and the oil presumably gets sucked into the motor during the next start rather than leaking on to the bottom of the carb.
I have also stopped using the side stand for overnight parking.