I think you are talking about the big nut on the side of the oil pan Brian? Where the dipstick tube goes in?
Bad design, the more you tighten, the worse it will leak.
The o ring seal is on the inside of the pan. The nut pulls the flange against it and the pan. There is a cheat so you don't have to pull the motor. But if you take that nut off, you have to capture the part to keep it from falling in the pan. Engine removal to retrieve after that. Some say a brass brush for gun cleaning in a calibre (don't remember which one) that will be a tight fit with a string attached does the trick so you can remove the seal, replace it and then the nut. I imagine same could be negotiated with a needle nose type vise grip holding it.
You Tube is your friend with a lot on a 7.3