A guess ventured....
From my rather limited experience of the 4.0 motor, I would suggest it is the valley gasket. In your second photo, look for the thick, black plastic loom that holds the wiring harness. Underneath that is a metal strip, bolts running through it, securing a rubber gasket that spans the front edge of your valley gasket. I believe oil is seeping past that gasket.
The bolts holding the metal strip are worth a slight tightening. But leak will likely continue. You can see that changing the whole valley gasket is quite a job!