I took the phone apart and the whole inside was filled with 40 year old cobwebs, dial and all. I cleaned up what I could. The problem isn't the dial spring after all; it was in the gears behind the dial. It may have been the wrong thing to do but I gave the dial mechanism a liberal blast of contact cleaner and then some compressed air. The dial returns freely now.
Yes! Taking my finger out of the hole after turning the dial helped too. Thanks for the tip, Bill.
