You may only have a rust problem but...just for you to think about.
Chain plates have a life limit, just like the rest of the standing rigging
. It's metal fatigue. My rigging lasts only 5 years but most goes for 10 years, depending on a lot of factors. Even at anchor
your rigging "pumps" from the rocking motion.
Do you know when they were last replaced? Perhaps get a rigger to inspect it and all your rigging. I know what to look for, inspect every morning at the deck
and several times a year up the mast
, but I always pay to get an independent eyeball on this once a year. You can replace the rigging yourself and have new chain plates made at most machine shops. Just something to think about.