THe 87 manual
Does state this:
"Keeping the keel in the raised position will help prolong the life of the flexible stainless steel cable by keeping as much of it out of the water as possible."
I tried this method in a freshwater lake at a slip and after two seasons my cable was dangerously close to breaking from hinge action at the ball. The cable had several breaks in the strands at one location that you can't observe from topsides. The turning ball also had developed a fair flat spot in one place from the fact that the keel will pivot in any possible direction at that location. This includes L/R (Port and starboard) and rotating with regards to any play in the pin and hole from the front end. This will happen with every wave that the boat takes from the side.
Keeping in mind that it appears that C22 manual is very concerned with electrolytic erosion I think that they didn't address certain other friction issues.
I feel that the more that the boat is rocked while at rest, will increase keel wear. This wear will be exacerbated if the location of the cable is the same all of the time. For example, if the keel and cable is always in the up position. This is why it's my suggestion that although only careful scrutiny of these parts on every fall outhaul of the boat and occasional checking of the cable while in the water is the best prevention tactic it may also be a good idea to vary the location of the keel to spread out this wear factor.
One way to decrease the amount of rocking may be to lower the keel all the way but I don't have my option at our fairly shallow dockage. It can get to be a tad less than 4 ft at times. By lowering the keel it will do some to limit the rocking action, it may transfer some of the strain to the pin and keel hole area. Remember that the hole through the keel is remarkably close to the top edge and it can wear with time and action. I'd recommend having a plan of regular check of these parts no matter how difficult this is because safety is a first priority. You' also want to shim up between the keel and the keel trunk properly to limit the amount of movement at this point Because this is a point of friction. Another issue is to try to really not ground out the keel while sailing. I suspect that if the keel bounces over a rock and then drops to the cable, this could put a great strain on the cable itself, stretching it or possibly causing it to snap.