[P.S.]

Pretty sure there IS a gasket between the banjo housing and the torque tube. If not, fluid would leak here since the fluid level is above the bottom of the torque tube hole in the banjo housing.

As for venting the rear diff... One of the guys in a neighboring club did that before heading to the east coast in his Model A. Blew the rear end after it went dry due to losing too much fluid out the vent. When driving, the differential fluid is flung all around the inside of the banjo housing. The goal is to keep it in there. Leave it stock!