Any good parts supplier should stock them. Try National Seal #411330 N. Thats a zero, not an O. This should be a double seal with a 1/2" felt packing sitting in front of the pinion seal. You dont need to make a new felt seal but I did on mine.

Jeff


My 1953 Chevrolet
1947.1 Gallery
1972 C-10 1/2 Ton & 1972 C-30 1 Ton