The driver's side rear of my '74 Bus was always around 3/4" lower than my passenger's side. Today I adjusted it so now it sits even - took me three tries to get it right . When I pulled the torsion bar out (it actually came out with the spring plate because it was rusted to the splines - it came out with a few taps of a hammer though) I found it had a bit of rust on it:
Is it weak because of the rust? Should I replace it?
I wouldn't be too worried about it, doesn't look that bad to me. You could polish it with emery cloth to remove the rust and then repaint or grease it. If you are worried about it, then for peace of mind replace it.