Chain plates

[Brion Toss]

Hello,
Pardon the alarming heading. More exclamation points than absolutely necessary. But what you are describing is the single most likely cause of a dismasting in a sailboat rig. The fact that you have had leaks only amplifies the likelihood; it is almost certain that a good bit of that water has made its way into the pocket that the chainplate is sitting in, and the metal has been merrily crevice-corroding away for a long time. How close to failure do you think it might be? Oh, and there are other things that kill chainplates, like salt, fatigue, and less-than-optimal alloys. All of those have been at work for the past 30 years, too. There is basically no way that these chainplates can be considered trustworthy.
It will be difficult to address this problem. You might be able to bypass the current location and install new chainplates. You might be able to carve away the existing setup and install something rational. But it is clear that you need to do something. Soon.
Fair leads,
Brion Toss