That's not discolouration or wear.
This movement does not hack in the traditional manner when you pull the crown out to set the time. To sync the time to a known standard you use a stylus to depress the button that is in the center of the crown. Quick pushing of said button will advance the second hand by a second for each push, or if you push and hold the seconds hand will stop.
Also, if you push the button in and hold for 5 seconds, then release and quickly push it back in, the minute hand will rapid advance.
There is nothing wrong with the crown.
Cheers, Al
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