My Westsail32 Immamou has been afloat on a mooring in Chichester Harbour UK for two seasons. I found rust staining coming off the lower aft chainplates staining the white gelcoat. Looking unsightly I've  decided to replace the chainplates. I was advised the rust was probably from the bolts thought to be sub standard A2 stainless steel. Removing the starboard plate it snapped off at the top bolt just below the capping. Its been cracked for ages. I think the chainplates are original from 1973 Just thought I'd post to make others aware.of the issue. See pictures

Ed: 

Thanks for the pictures  - I've added your pictures to the Google Album Items that Break

Members Area also has a link to this album from this page. 

Glad you got it replaced in time - I assume you have removed and inspected the other chain plates.  Here is a link to a topic on chain plates.

Jay