Welcome!
It sounds an unusual problem. Have you had a chance to check the condition of the saildrive and more importantly the saildrive anode for degradation? It’s quite normal for the anode to gradually erode over time but usually it will require replacement at the end of each season. If the anode has completely eroded away then the next thing to go is the saildrive itself, which is definitely not a good thing! Also, it’s most important that the engine itself is electrically isolated from the gearbox and saildrive units; if for any reason the engine has been separated from the gearbox and replaced without the special isolating gasket and insulating washers for the securing bolts then it would be possible for electrolysis to start acting on the engine itself. Again, not good.
I too have a 2002 vintage 32 with the 2020 engine; even at 10 years old there shouldn’t be problems. My boat is left with shore power connected and on all the time and I’ve have had no problems like those you describe. I’ve often thought of fitting a galvanic isolator but while things remain as they are the boat seems perfectly OK without one. (She’s berthed in Chichester Marina, which I’m assuming has a reliable, correctly polarised shore power system!!)
I’m starting to get very hypothetical now, but does it look as if the corrosion is a recent thing or something that’s been happening longer term? If it’s recent then what’s changed to cause it? Also, I notice that you’re berthed in Ocean Village which has a lot of steel piling around its perimeter, this could theoretically be interacting with your boat. There are other BOA members in OV, might be worth chatting to them and also other boats near you to see if they have any problems.
Sorry I can’t be more helpful…
Ian Culley
B32 Another Fantasy
