Thanks for your comments guys!. fonzi, by the time you notice the differential seals are leaking you might have lost most of the oil and if you continue to drive the bearings and pinion cogs get overcooked with the corresponding very expensive replacement!. Your 73 needs the same procedure.
One of the contributing factors to leaking seals is that the breather valve gets blocked and the oil pressure build up pushes the oil through the seals. I would strongly suggest to replace the oil in the differential and thoroughly clean the breather valve and filter until you can schedule the seal replacement.
Unfortunately MB don't sell the filter alone but the entire valve. The filter is just a piece of felt to let air out and prevent the oil seeping through. My filter was beyond retrieval, so I used one of those adhesive felt pads, removed the sticky glue by slicing with a razor blade and trimmed to size and you can blow easily through.
Notice the amount of muck and crude accumulated on the filter!