You could be right...the voltage potential is just so overwhelming everything goes....
I can't find a lot of logic in most of this....
I've just antifouled and refurbished the Autoprop with new bearings...and after seeing the shaft corrosion on (your?) shafts, I've installed the prop zinc that comes with the bearing kit... I see the 54s have it whereas our SM53s don't ...why ??
Also I showed those pics to an engineer here and he thinks it is crevice corrosion caused by Stainless steel operating in an oxygen deprived environment...which could be the case if the outer seals failed, but the inners didn't....more food for thought.......
SV Elyse SM437
Gulf Harbour NZ ...currently