It’s not just the bronze that has this issue.
I have a BB red ETA bought off this good forum. The crown tube had pitting as a result of galvanic corrosion (most likely from use in sea water). It was well out of warranty but Tudor replaced it free of charge.
They recommend that all black bays are washed regularly to remove any sea water / sweat which can cause the issue where the stainless steel meets the aluminium.