Hmm now that I think of it when replacing the cable and getting my eyeball looking up into the tube it had a slot that yes the cable has a small sheave and I guess thats where it lives when the board is up.
I also should note to others with this set up that right above the sheave where the cable crimp is is the spot where the cable fails cause the board moves while sailing and thats where the cable gets the most fatigue.
The last time I replaced the cable (spring 2009) I installed a foot extra so this spring I'm going to cut 6 inches off at the keel end and redo it with a new sheave and crimp and thats when I'll take some better photos cause this subject has come up many times
Rad,
Before you do anything about this cable, you should call Rudy and ask him if you can convert that cable to a braid line with a shackle. I'm almost certain you can do this. Rudy had told me quite a while back that the cable on the 1975 O'Day 25 can be converted over to braid line. The centerboards are only made of fiberglass just like the centerboards on the later model OD 25s and 26s which are set up like mine in that the braid line comes up into the cockpit. The 1975 O'Day 25s have a winch drum on the table pedestal down below. We have one at our club that is set up that way. Whether the guy who owns it ever converted it over, I don't really know, but Rudy had told him that he could use braid if he wanted to. This may apply to your boat as well, provided that the pendant line can go through that sheave. If for some odd reason the sheave is too narrow, you can remove it by taking the nuts and washers off from inside the cabin. The sheave and U bolt can be removed from under the keel. You would need to Mickey Mouse something to grab it. Rudy also has the sheave and U bolt set up for the keel slots, but all you would need is just the sheave, which you can purchase anywhere.
The one good thing about braid lines is the fact that it can be inverted just like halyards and sheets and anchor lines. I've done all of these through the years. You only need to remove it with a tag line left in the pipe and make up the other end for the shackle. Then cut the old eye splice off and use the line over. I'm not as familiar with splicing braid as I am with three strand rope because I don't do enough of it. So I go by the directions when I splice braid. I've found that these braid centerboard pendant line really don't wear that much. The only thing that I had to replace last year was the cotter pin on the shackle and that was it.
I may be all wet on this braid line conversion on your particular model O'Day boat, but it's worth checking into I think. It's just food for thought.
Joe
She’s also beautifully designed on the exterior with exquisite lines. It’s funny, that boat is just shy of 30 years old, and I think the design is more impressive than a lot of newer ones I’ve been looking into. 
