Thanks for the comments. I can respond to some of the points made:


It's true that there are lots of these boats around here, and lots of
collective wisdom. Opinion 2 came from a respected rigger with years
and years of Santana experience. He replaces the stock aluminum
chainplates with 1/8" stainless.
Schock also sells new chainplates now that they are selling new
santana 22's again, but the bolt pattern is different on the new hulls
so I would have to mess with the bulkhead. Same case for the standard
Schaefer plates.
I'll look more closely before buttoning everything back up, but the
plywood seems to be in pretty good shape - some varnish has
dissappeared, but no apparent softness in the plys or raised surface.
I do have slotted caps and will caulk well.
I'm not wild about going to mild steel/paint or spending much money or
effort improving the ones I have. If I'm going to mess with it, I
want less worries, not more.
The $200 quote was for 316 at a generic machine shop - I had to
describe what a chainplate is and does, I take that as a good sign but
I probably should have just said it was for farm equipment. I didn't
ask them about 316L.

My gut feeling is that if I don't replace them, I'll probably worry
about them enough that even if there is no spectacular failure on the
bay, the $200 would have been worth it.
I'll have to check with a friend to see if he can handle stainless in
his limited backyard shop.

McMaster-Carr's price for a 2" x 36" x 1/4 flat bar of 316 is $42
plus shipping. They don't have the 316L in 2" bars so I would have to
cut down a larger plate, for $65. Local would be a better bet anyway
to avoid shipping...

Thanks again. I appreciate all the fast responses.
Joe