I have a 73 Duster with a /6 and Auto 3 spd, and the differential leaks excesively. Is this normal?

nn2004@peoplepc.com

No, the rear end should not leak a single drop of oil.
You most likely have a bad pinion seal or a leaking cover gasket.
Clean the unit, refill and check it closely to see where the leak is coming from, then replace that seal / gasket.
DD

This may only be applicable to the 8 3/4" rear, but I'm sure someone will chime in if that is the case

On the driver side of the axle, there is a "T" fitting on the end of the rubber brake hose. The screw holding the fitting to the rear end is actually a vent, and if this vent screw is clogged then excessive pressure can build up in the rear end and cause a leak.