And we have a winner!
chances are you measured correctly (especially if they didn't snapped back perfectly straight but kept a little bow)
and they're simply worn out.
A new driver is not necessary though, new weights and springs
(20 bucks set) will solve that issue.
If you replaced the weights at any one point and the wear mark is still crisp and complete you could also reuse the weights even and just buy new springs (10 bucks for the set of two springs)
but since you already ordered the driver that'd do just as nicely of course.
'sid