i don't have any parts literature on this model but from what i remember on these drive MDU's is that component your pointing at in the picture is a pin that supports an idler gear inside the drive unit. It presses into the case into some bearings and is shimmed too i think so it sets a preload on the gear/bearing it corresponds with. As far as the leak? I'd say that it was not properly sealed when assembled and if there is oil coming from the center 'threaded' hole then there is an issue with the pin. That center hole is only there to provide a way to insert a tool so it can be removed using a snatching tool. if i remember there might be an oring sealing the outside of that pin and it could be bad allowing oil to come out. I would clean it up with some brakecleaner and run it and make sure where the oil actually is coming from. Of course if it actually is coming from the center hole then the pin might be damaged and would have to be replaced to stop the oil leak.
Just FYI, if you try and remove that pin without removing the top of the mdu then the gear on the inside will fall down and you will have a hard time getting it back in place and would ultimately have to take the unit apart anyway. If you've never done this before i would get some assistance from someone that has.