You can also use the 90 weight mineral oil in the differential. My engine was compeletly redone about 31 years ago and I have always used straight 30 weight Castrol, non detergent, and I only change it once a year and at each oil change I add about 5 ounces of Risolone zinc additive. It is near impossible to find regular oil in the parts stores, so I buy it off Amazon, 6 quarts at a time.
Also when I was doing the initial restoration back then, I used Silicone DOT 5 brake fluid. I have had NO issues in all that time. Okay, it's a garage queen, goes in and out of an enclosed trailer, and sometimes gets driven on some country roads.
Later,
Glen
1938 Chevrolet half ton pickup
