gearbox lube??

After Walt Mordenti rebuilt the '50(?) single-lever box in my Hornet he reccommended using synthetic. I had it filled with 75W-140 and it has never performed better. It especially helps on cold mornings when I use the car to drive to work. Have put about 4K miles on it, mostly short hops around town and trips of less than 100 miles. It seems to do much better than with the old 90Wt. Hope this helps