At the end of the door check rod is a rubber stop that ensures silent operation of the door. If they have never been replaced before, you can assume that they have dried up in the meantime. As a result, they can no longer fulfil their role as shock absorbers.
Volkswagen has never made this rubber available as a separate part, although an official part number has been assigned. At the time, you could only order a complete door check rod from the dealer, but not the rubber separately. They are now available separately so you don't need to buy a complete part.
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