I've seen something similar on my 1980
I have seen simultaneous flickering of several "on" indicator lamps (LEDs?) on my DC panel. I doubt that's the same condition that you've seen. It doesn't happen all the time. My electrical panels are both after market mods (well executed in 1995) that the PO installed. I have not seen the AC service lamp flicker, though, that I can recall.
Ted's suggestions were pretty good. Many marina fingers have grounding problems and unless you compare with other fingers or can put an oscilloscope or some other AC analyzer on the power source, it may be hard to figure out what is going on. When I was in the salt water at Shilshole I went through zincs in 4-6 months. I even dangled a grounded zinc plate over the side all the time in the dock.
In the brackish water of the Duwamish River mouth I go through zincs much more slowly, 8 months or more per set. How fast do you go through zincs?
When I get back from this trip Saturday and recover from this crud I picked up (and get over the Seahawk game on Sunday) maybe I'll have some more ideas.
Hope you can figure it out, but it's hard to tell if it's serious at this point. Are your neighbors reporting anything? You might also ask the marina maintenance people about it. There could be a temporary, or a new, power condition that has nothing to do with the finger or slip you're in.