Possibly oil cooler? It is on the drivers side. I just fixed the oil cooler on our work truck and it dripped off of the front axle, but everything, I mean everything on the drivers side was coated in oil, quite messy.
Other than that I would think the oil rail plug, like stated. One of them let loose on our work truck, it just poured oil. I am sure they can just leak a little bit though.
Your best bet is to degrease the area where it is leaking and let it run so that it leaks and find the wet spot. Or you could use dye in your oil, not sure where you get it though. You also need a light to illuminate the dye. That is what the place that works on our truck uses to find oil leaks.