Berrien Springs, MI
The ULN2803 can handle up to 50V on the outputs (and up to 30V on the inputs), so the unregulated voltages you are measuring are not an issue unless a short to one of the power rails is present (usually why they blow up).
Any time I hear "lightning" or "sea water", I'd be suspect of any of those boards working correctly, even if a pro went through them. The very first thing I would do is swap out the CPU board and see if the problem persists. This way you can eliminate any possibility that corrosion or other chip damage (pre-driver TTL, etc.) is an issue.
