4 screws and knobs off, Pop the cover and look at rollers/windings. Rollers must roll, never skid, windings show no sawing or heavy wear.
Rollers can sometimes crack and it was just shipped
And I trust MY eyes more than the guarantee. The guarantee is just the fallback plan.
An experienced hand might feel all 4 for "bump" ease/consistency.and try to notice any significant changes over time and/or in time to "save it" again.
I love my old Z The insides are pretty cool with the arm/gears/shafts to reach under the winding bottom, etc.
There is a rare KW with a similar gear set up. (maybe a pre-production prototype vs "rare", but I had one as a kid)