I would not run my HD-25’s in salt water, no matter what. I wouldnt recommend it to anyone. I would fear for my driveshaft getting ruined

I may take some flak for this, but IMHO you won’t harm the HD by using it in salt water periodically. (We are talking about the Atlantic or Pacific here, not the Great Salt Lake or Dead Sea?) As long as you wash it off afterwards and run it in a freshwater test tank it should shake off the salt like a duck. Heck, until I was 18 I didn’t think fresh water was for anything but drinking! I had a vague idea that in places like the Great Lakes and Minnesota there were 2 or 3 people who boated 😉 but the vast majority of boating worldwide was/is on salt water – and that’s where all my antique and classic motors were used up ’till then. (And some still used!) People in salt water places also deserve the fun of seeing a nice classic motor run!

I have a TD and a TN that I use each year at our Mystic Seaport meet and neither of them have seen any ill effects from use in Salt. Okay, I wouldn’t recommend it for a Ruddertwin, Clark Troller or a rare and valuable antique/classic like a Amphion, Cross Radial or Amarc. But the HD is a really common motor and Johnson did a pretty good job with their corrosion protection for that time. Actually, an HD or TD that had the L/U fasteners preped by a dip in Permatex or another silicone sealer, would probably hold up pretty well even under relatively long term salt exposure. It may even hold up better than many of the new motors do! I have a "dump find" 1965 Johnson CD-22 6hp that is used as a trolling motor on my Mako 19 that’s pretty much only seen use in salt since it was new in 1965. Properly prepped, waxed each year and washed off after use, it’s fine and still even sports 95% original paint!