Scientifically, brass and copper both are subject to discoloration from oxidation. However, oxidation of these rhodium plated brass plugs is strange. Stating the obvious, rhodium and gold are used for oxidation resistance while not affecting electron transfer. While brass is a less expensive option that does not transfer electrons as well as OCC and OFC four nines copper, the brass is more resistant to discoloration from oxidation than copper due to zinc in the alloy. If you are a boomer like me, think of the rot cars used to get after a few years compared to today. The reduction in car rot (steel oxidation) is due to zinc phosphate. I have only used Furutech rhodium plated OCC/OFC connectors and I have no experience with this cable brand. Others post good experiences. I have not experienced oxidation of Furutech connectors. So, from a quality engineering perspective, potential causes could be:
- A plating processing problem at the manufacturer. Either the coating thickness is off or the plating process parameters were not in validated ranges.
- Issues with the brass base material. The lot of brass (termed a heat lot in metal production) may have produced material not specification or at the upper or lower tolerances, causing it to be subject to a faster rate of oxidation. For example, a lower level of zinc.
- Ware from use (plugging/unplugging often).
- Chemical reaction with contact cleaning/enhancing or oxidation removers.
- Inadequate male/female connection under high current, causing heat that, in turn, accelerates oxidation.
I hope this helps you prepare for your discussion with Raven so that they do not attempt to make this your problem and not theirs.