Yup, davkol points out that the actuation forces from the spring have a tolerance zone and aren't perfect. The sliders, springs, and the points in the housing that contact the sliders should wear. I think if you had some calipers, you could take measurements to check the dimensions on the sliders. Compare those to new sliders or specs on the Cherry site and you'll probably see differences.
If someone had access to a lab, you could also figure out some mechanical properties of the spring and see how they stacked up to new springs.