Have a Hudson with a 3sp OD trans that has the wet clutch. Can buy the "Hudsonite" clutch fluid but if there is a modern fluid readily available at any parts store would rather go that route.
Contact Doug Wildrick at Wildrick Rubber Products at www.wrphet.com Trust me when I say he has everything for a Hudson that you may need. First Class Hudson nut to be sure.
ATF for older transmissions works. If it's leaking, you're probably going to end up replacing the clutch and TO bearing anyways in the near future. Just don't let it get dry, and it'll keep going for a while.