A 2024 update:
I have a 41-47 Muncie 3 speed floor shift in my 46 1/2 T pickup. Got the usual oil leaks from the transmission and some from the rear engine seal. When I pop the fill plug on the differential, I get a load of transmission oil. After a while, not much in the transmission.
So as I understand, oil misses the front oil slinger catcher washer (and leaks out the front), and it misses the probably missing felt wafer in the back. The back one is supposed to keep the oil forward. So the oil runs down the driveshaft tube into the rear end.
I have it in to a local transmission shop that said they could work on it. When push comes to shove, they really don't know/can't.
On the advice of DavidF above, I made a call to Pistoles to leave a message. I had an absolutely wonderful conversation with Sunni Pistole. Turns out he has a couple old trucks he fiddles with similar to mine. Our rotations around the sun are also about the same. We went thru a lot of things that could be done. Both engine and transmission. He explained to me what has to be done to these old iron machines to "fix" a couple of the problems above. It ain't for the faint of heart. Either the engine or transmission. And it isn't a simple bearing or seal replace like a wheel seal. And it is fraught with doing things and possible ruining things that are hard to find and replace. And in the end, you most likely won't end up with them being oil tight. They were not designed to be that way in the beginning, so it is unlikely it will be that way after years of wear and a few replacement parts. But it happens, a few sometimes.
In the end, the expert that does this for a living said to me ABOUT MY PARTICULAR SITUATION, "If it were me, I'd get a couple oil catch pans to catch oil when it is parked, and periodically drain off some oil from the differential and put it back in the transmission."
Sometimes in dealing with stuff with age, it is what it is and that is about as good as it is gonna get without a whole lot of pain, time and money, that may or may not improve the situation.
The same can be said of old vehicles.
