If you open it up and clean it...
you can look at the WEAR PATTERN on the gears....
I suspect the FSM shows a good pattern.. but this is not different for other cars...
To clean I would open it up on the back side... tilt it
slightly backwards.... and spray with a hand oil gun... while turning it slowly....
Then wipe out all that on the base with blue non lint paper towels...
For instance...
https://www.google.com/search?q=hand+oil+can+pump&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwig3L22x6zUAhVIilQKHcpGBzIQsAQIvQE&biw=1024&bih=615&dpr=1