Mike,
The centerboard pendant lines are usually made up of low stretch halyard type braid line like Sta-Set x. Snaking a line down the pendant line pipe on your O'Day 25 should be fairly easy because the line runs right down to the centerboard with no sheave to run through at the top of inside keel slot.
My 1986 O'Day 222 has this sheave as does the O'Day 26.
Actually, $31.00 for a centerboard pendant line isn't a bad price considering that the shackles go about $15 or $18 and you're getting the braid line with the eye splice.
I often make typos on these forums myself so take heart because they can be corrected at any time you wish. All you have to do is click on to "Edit Post" and correct it. Where it reads, "Reason for Edit" you can put in "Typo" or "Add more info" if you have more information that you want to add to the post.
On numerous times I've developed a severe case of "Brain Gas" which quickly prompted me to delete the post altogether.
Joe