I had a broken rear main leaf, and the other side had a bend between the shackle and second leaf. The unbroken side had notches in it from the second leaf digging into it. I found a pair of tonner rear springs in a junkyard that were only slightly notched and had a good curve to them. I disassembled the packs (which is a good idea if you find any rust in the centerbolt), and ground each leaf smooth with an wire cup brush on an anglegrinder. Eventually I got all the rust, burrs, and notches smoothed and I beveled the ends of the leaves (a bit more than they already were). Then each leaf got a bath in WD-40 to keep the rust off and a new centerbolt from Tacoma Screw was used to hold them together.
If your truck has been overloaded, it will have bent/flattened springs. Replace them. If it's just old and the notches aren't deep, you should be able to grind them smooth and reinstall. Remember to lube the springpacks with the rest of the chassis and they can last forever.
