The rest of the story.

1997 arrived in New Zealand. Pulled the mast for overhaul and painting. Since it was out I pulled the chain plates. Core was wet around the chain plate cutouts. Chain plates looked rusty where they passed through the deck but with a little cleanup looked OK to the eye. To be sure I had them dye penetrant tested. The guy that did it showed me a tiny hairline crack and then proceeded to bend the 3/8 inch steel with his bare hands. The cross section was completely riddled with rust. Of seven chain plates three had similar cracks. I had all seven copied.

The wet core was rooted out as much as possible and the gap filled with thickened epoxy.

Forestay chain plate was part of welded up stem head fitting and looked OK. That was not replaced.

Flash forward to 2007. Back In NZ. Had the same guy test and electropolish the now ten year old chain plates. He said the looked as good as new.

PPS. Al, thanks for the comment about 316 vs 316L.