That one bushing probably seized up on the shackle pin and spun within the spring. You might try clamping the leaf spring eye in a BIG vise and squeezing it a bit. Since it's spring steel, it will take a lot of movement to bend and stay enough so the bushing is tight. Another band-aid would be stud and bearing mount type locktite. But I predict that fix is probably not going to last.
The correct approach would be to replace the springs with new. They'll come with new shackle bushings installed. The originals are likely sagged a bit anyway.
