[M2M]

Originally Posted by dumb person

The bottom leaf holds to the axles. If you have doubts to it's strength, then replacing it is a good option.
It's only a bad option of the other leaves are rather poorly, as they do the heavy lifting.
So to answer your question, if you feel you lost bounce, the bottom one is only the first one to change out. Uppers may vary.

Originally Posted by Randy in ca

There’s no doubt that the shape and condition of the leaves above the main leaf has a definite effect on the overall shape and performance of the spring assembly. Each leaf moving from bottom to top should have a tighter curvature. That means that every time you add/clamp another leaf above, more curvature should be forced into the leaves below and the main leaf spring eyes become closer together. By example, all rear main leaves should have the same eye-to-eye distance when loose, but by the time they’re assembled those springs with 2 or 3 more leaves should measure up to 2” shorter eye-to-eye due the additional force applied by the curvature of the additional top leaves. The Roadster spring, with the least number of leaves, should have the flattest appearance when assembled as well as the largest eye-to-eye distance. An old catalogue I have shows the assembled Roadster rear spring eye-to-eye dimension as being 40" to 40-3/16" while those for other models range from 37-7/8" to 39-11/16" eye-to-eye when assembled.

Good answers that directly address my question about replacing only the main leaf with a new one.