That is a pretty common place to see a little oil build up. There is the valve cover gasket just above there, the plastic disc that seals off the hole to access the cam gear, and the oil pressure sending unit, and oil filter, all right there. Sending unit and filter looks dry, valve cover looks only slightly wet. My vote is the plastic disk that covers the access hole for the cam gear. They really arent to snug in there sometimes. I would get some carb/choke cleaner and clean that area real good, then watch it and see if you can tell a little better. If it is the disk, just clean the area real good and smear a little RTV around the edge and run it.
'00LMTD-4.7l,242hd,D30,D44A,3.73's,True-trac front,Spartan rear,4" short arm lift,JK'sW/32's