For all those who struggle with sticky rubber parts and knobs:
I just found on the German Ebay an offer for 3D-Printed knobs and replacement stickers for the other rubber parts.
I have not tested them, however this seems to be an innovative idea to solve the issue.
There are many photos showing the procedure and a detailed description in German with the limitations and advantages...
The sellers name is "donscore"
You can find the offer at https://www.ebay.de/itm/Squeezebox-B...f/153792458381.
He also offers 3D- Replacement knobs for the radio...
In case this works, let the community of sticky knob know....