This is a common issue with any sort of spring loaded end link. The damage is most often seen on softer cases, like this one that is 18k gold:
However, stainless steel cases are also affected:
Since there is nothing on the end link to keep it from moving relative to the case (as there typically is with fixed style end links) the relative motion of the parts, plus the pressure from the spring will eventually damage the case.
I usually advise my customers to avoid this sort of spring loaded end link, and people here have developed various work arounds to protect the cases from damage, such as fitting O-rings between the end link and the case.
Cheers, Al
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