Well, if you know it's coming from somewhere above the oil pan and rear seal, but below the heads and sender... does it matter which plug is leaking?...lol. The engine or trans needs to come out and that's that. But I'd make damn sure it's from the back of the block first.
BTW I should probably admit at one point I pulled the trans, clutch ,and bell and replaced the cam bore cap thinkign the seeping was my leak. Then I found out it was the lower 1/2 of the rear main that I have put in the retainer backwards...