This is an interesting challenge. A couple of points:

  • Judging from the materials in the archive, reports of failed steering control cables seem to be quite rare (and I don’t imagine that is because they have always been replaced in a timely fashion).
  • Over the years, many other boats must have been kept on swinging moorings, so that in and of itself is unlikely to be a major factor.
  • Have you considered the potential role of the tension under which the cables are kept? Could too little or too much tension be part of the problem?