It can either be from two sources inside the clutch assembly.
The pushrod which comes from the other side of the engine has a series of small o-rings on it, and one of these could be failing leading to oil coming out of the very centre of the clutch.
The second area is behind the clutch assembly where a large flexible seal is pressed into the side cover. Although not known to cause problems, this could also be a source of the oil.
Cheers.
Lee.
http://www.monstershop-ducati.co.uk