Ummmm, that pitting looks pretty serious. If it were me I would replace it with something like a Posies Superslide spring. You will get a better, smoother ride, and by picking the right spring you can lower the truck a little too.
I really think that one you have has seen better days, and if the surface isn't as smooth as possible the leaves will not slide on one another like they should. It will be like the suspension is welded solid.
Don