I would de-grease the crankcase with some gunk and then try to pin point the leak. Take a look at a parts diagram if you need info on gaskets, seals, etc.
Try Kawasaki: https://www.kawasakiepc.com/SystemSearch_Frames.cfm?QuickSearch=1&SearchFor=KEF300%2DB3&SearchBy=Model&cGroupID=&CFID=1300276&CFTOKEN=39824260