The transfer case has to come out to get to the transmission. The question then is whether you can replace the seals without tearing it down further. Personally, I would probably want to disassemble it at least partially to inspect it. See if the bearings, races, and teeth all look good.
You...
What @jonheld said. Seems somewhat common over in the 40/55 forum.
https://forum.ih8mud.com/threads/transmission-pumping-oil-into-transfer-case.85619/
https://forum.ih8mud.com/threads/gearbox-leaking-into-transfer-case.351673/
It's a band-aid fix that may not even work...