Definitely leaking from the plastic plug/insert that holds the stator wires and crankshaft position sensor. I have attached a pic that shows the plastic insert relative to the crankcase cover. There is a thin paper gasket runs all around the edge of the cover except the plastic part. There is no gasket or sealant around that area. It simply goes hard from heat and oil can leak out while the engine is running.
I wouldn't worry about to much, oil can't leak quickly since it is on the top. Clean it and apply gasket maker. If you ever take the crankcase cover off, the gasket maker will work better for the leak but the paper crankcase gasket will rip, so get a replacement beforehand.
Source: 80,000 km on a DT300i and my new DT350i is starting to show a smear from the same location.