Sunbird! I just went outside and examined the pivot hole. It is very clean and round, and about 1 1/8" in diameter. This is one clue that your suggestion is correct, for one would expect a worn centerboard hole to be out-of-round (considering the board hanging down always, it should be elongated in an up and down direction, I would think).
Another clue is that my CB rod is somewhat crudely sawn off on one end... like someone did it roughly, in a hurry, with the wrong saw. This is very different than the very nice quality of finish on just about anything else on these boats.
A third clue was when I checked the online image of this arrangement (not sure where it originated, but an O22 owner here, I think)(my apologies for using the pic, and thank you), and used my graphics program to "move" the diameter of the pin to the width of the SS plate for comparison. Yes, not perfectly scientific... but since the pin in the picture if further back, and since it is very slightly elongated left to right from the angle, it should appear smaller in comparison to the wedge retaining plate... but it is still bigger. See pic:
As I said, not scientific... but from all clues I would guess the pin was replaced with a too small one (found in a hurry probably... marina shop? local hardware?), and that the pin should be 1 1/8" or thereabouts. So I'm going to order a 1 1/8" Delron or nylon (haven't decided yet which) rod on eBay, and give that a shot. I might turn a test rod on my lathe first, in wood, just to see the fit in the hole, before ordering.
Thanks much for the tips...
Edited to add: Setting up the lathe would have been over-kill... I simply wrapped my 1" pin with stiff paper until it was exactly 1 1/8" in diameter, and taped it. Then I went outside and tested it in the CB pivot hole: A perfect fit! Slid right in, with just exactly the barest amount of play one would hope for! So that is the answer... the rod was replaced, and the hole is not worn. Happy days!