After some days of use: The counter struggles incrementing when a carry shall happen:
009 -> 010 doesn't work properly anymore. Instead some clicking noise is noticed.

To check, the front panel has to be removed and the suspect is visible:

The attached belt seems to be ok - after unplugging the belt the issue can be reproduced by turning the counter wheel.

To stop the annoying counter-clicks, the counter has to be removed until a replacement is available.
Since removing the belt would require some more disassembly I decided to fix it:

Re-assembling the front cover is a tricky part - the four knobs swing and turn below the cover.
They require some fixation before applying the front again:

Counter is gone

and needs furhter analysis