Check to see if the oil filter housing is leaking where it bolts to the side of the block. My understanding of the rear seal is that it is a two piece rope type. It is mounted in the rear main bearing cap and block. You would have to almost remove the crank.

__________________
My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.