If you're not in the habit of leaving your centerboard down when your boat is at the slip or mooring, I wouldn't touch any of it. Wedges and plates never need replacing. If the wedges get a little damaged, you can reconstruct them with epoxy and filler.
I suppose it wouldn't be a bad idea to get the boat into a position where you can let the centerboard down and check it for sloppiness. You're going to have some side ward play on your board. My board has it and I suspect that they all do. Just grab the board and push it toward the pin back and forth. This will give you some idea of the condition of the pin or the hole in the board without pulling the board completely out unless you want to pull your board out and that's OK.
I pulled the board out of my 1986 O'Day 222 years ago and found nothing wrong with my pin. It gave me a chance to bottom paint inside the keel slot and also gave me a better understanding of how this system works. I thought it was pretty ingenious myself. Check my Photo Album on this site for pics of the whole set up and some tips and ideas on how to remove the board.
I'm pretty sure that your centerboard is set up the same way inside the keel slot with the exception of the sheave in the keel slot and also the pendant line.
Your 1975 O'Day 25 has a cable coming off a winch mounted on the table stanchion down below and it's a straight shot right down to where it is attached to your centerboard.
My pendant line comes down from a step in front of the companionway in the cockpit via an "L" shaped pipe to a sheave in a small pocket tucked up inside the keel slot. The O'Day 26 has the same set up.
Your centerboard being Fiberglas is no heavier than any later model O'Day 25s and you can very well replace the metal cable with a braid line on your winch. You may want to talk to Rudy at D&R Marine about this.
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My pendant line has a long shackle at the end of it that is attached to my centerboard. I'm not sure what you have at the end of your cable or how it is attached to you centerboard. O'Day Mfg was forever making changes back then.
I would be more concerned with the condition and attachment of the cable to your centerboard if anything. It doesn't hurt to check it and this is the best time to make repairs to it if it needs repair. If the cable checks out OK, I'd stick with it for a while but if it needs replacing, I'd go with a braid pendant line instead of a wire cable.