We've had zero problems with the centerboard. There is a through hull for the cable that has a SS pipe & hose arrangement on it to guide the cable aft and up to the cockpit. I check the hose & fittings regularly, just like any other through hull. I've replaced the thimble and eye at the end of the cable once when I saw a few broken strands in the SS cable.
To be honest, at 110 lbs dry weight, the board applies very little stress on the cable. The only problem that I ever saw was with my Father's Catalina 22 back in the 70's. The fitting attaching the cable to the iron keel rusted through and the board came down with a crash. I though that the bottom of the boat would fall out, but there was no ill effect other than our stained shorts.
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I crewed on a Sabre 34 with the same arrangement, and there were no problems there either. If well designed, it's a reliable system. Just keep gunk out of the case - see the "What is This Thing" thread.