It's oil rfom the crankcase breather, it vents into the rubber tubes inside the airbox .
For some reason the left carb seems to be the one it leaks out of .
A few members here have positioned the clamps so that the adjustment screw is at the top, they say it stops the dripping .
If you keep the oil level at the top of the dipstick, that seems to ad to it, try running with the oil level at the mid-range .