NEUMANN U67 swivel mounts never fail, as far as my experience goes. What fails over time is the friction washer inside the female connector. This is a vital component that, if it is missing or dried up, will crack the phenolic Tuchel connector material, and render the connector insert dysfunctional.
don't believe there are any more sources for a new genuine swivel mount (Uwe Sattler may chime in whether there are any left to purchase). But they come up occasionally on eBay.