Well, it appears that the pans were tapped for 3/8 NPT during a "rebuild" in the past. The pan threads look nice, they are tapered, but a little over tapped so the hex head plug is bottoming out on the hex before the threads tighten up enough. I switched to an internal hex style plug to get that last turn and everything seems to be OK. The new plug sits just below the outside of the pan. Hopefully this is the last oil leak I have to chase

- ALex

Nope. Won't be the last. Pipe threads wear with each use. This was a butcher's brilliant idea. And the pan is aluminum. Those drain plugs eventually need welded or helicoiled. If you get them to hold oil, use a dipstick sucker to change the oil until time to pull the engines.

Ive had to repair these kind of hack jobs , I would get you some brass 3/8npt nipples with a hex on them.
Screw them into the pans , then use Brass pipe caps with a hex . That way you can drain the oil without wearing the pans threads any deeper.
Its a good stop gap till you can do the pans right.
You can also go too your local hydraulic shop and have them make you a hose , with 3/8 npt male on each end for drain extensions.