I would suspect the o-ring behind the housing. Other than the front oil seal, this is the only place oil can come out. Since the o-ring is between the oil and that particular bolt hole, I would have to venture that it is wore out or crimped. The o-ring is fragile and not always easy to handle when putting the oil pump housing on. A fine coating of vaseline, or even oil can help the o-ring stay in place while the housing is installed.

Richard S.
88 Toy 4x4 Truck, 22RE, 3"BL, 5-Speed, Muds
Proud to be an American. Blessed to be a Texan!