I've sailed on fresh water lakes for 40 years. We have no problems with electrolysis, crevice corrosion, or pitting. Our stainless steel doesn't tarnish. We don't get barnacles growing in thru hulls.

Those things don't necessarily "ruin" a boat and can be controlled by careful maintenance of the boatowner, so to think that a 30 year old fresh water boat that spent a couple of years in salt water is compromised is silly. My 1970 Mistral lived in salt water for 28 years, and after a bottom job and polishing all the stainless and replacing corroded brass fixtures below, it was fine.