The transmission oil should not migrate to the rear end. I forget about a 1951 (or any) pre-54 Advance-Design 3/4 ton having an articulated torque or having a partially open drive-shaft.
If prat of the the drive-shaft is open, no oil can migrate from transmission to rear end. If the torque-tube is articulated but fully enclosed, there would be a seal to stop gear oil migration between the transmission and the rear-end (just as the seal in the front end of the 1/2 ton torque-tube prevents migration of gear oil between the transmission and the rear-end).
