JimF, if you have fair access and can run the engine against the dock lines try a wire brush. With the engine running in gear you can hold the wire brush against the rusty stuff and things will appear as the rust is removed, try forward and reverse. You can also just use more "Norwegian steam" and just wire brush by hand if you have the energy. Whatever feels comfortable to you.
Spray some penetrating oil into the rust as you are brushing/or holding the brush. You will be surprised how much will come off~then you can see what you are up against.
Do you have the MMI manual?
Dave Neptune
