the morning net and ask if anyone has a "Salty Dog Electrolysis Meter". If they do, follow the directions and test for current until you isolate the break in your bonding system. Something is giving you a difference in potential between the binnacle and your ships bonding system. If you can't find a "Salty Dog test kit" you can improvise by using a digital volt meter and a chunk of, ideally silver, but realistically a big spare zink. If you had a silver tea pot on board that would work great but I doubt Annie has her grand mother's pot stashed. Fashion some long leads for the digital volt meter and set it to milliamps. Drop the zink connected to the negative leg over the side down about three feet. Connect the positive lead to your first through hull fitting and record the reading. Move to the next fitting and record the reading. Move to the next and so forth. Move to the engine block, the heat exchanger, your bronze sea strainer and now your Binnacle. You will sea a story start to unfold. All my readings are in the .35 Ma range. Start testing the system until you get to the break in your bonding system and then you will see a difference. That's the difference in potential that causing your pitting. Fix the bonding system and all the reading should be very close to the same. This is all from memory but I'm pretty sure it's right but then I'm old. I go through Brendon about once a year and record everything on a spread sheet. Year after year gives you a pretty good idea of what's going on. If you want, I'll go down to the boat and check my directions to be sure.