Most of the time the failure will be in the deck area so you won't see it until you remove the chainplates. Mine looked great until one broke 1" into the deck area. After removing a second one it was apparent that they all needed replacing.

Once they're out, why not just have the chainplate part that goes through the deck manufactured? 25 years is a long time. They're at the end of they're life.

Don't forget the headstay and backstay.