Well, that picture gave me the willies. I hadn't made a visual check on the hot pipe for a long time, just grabbed it and gave it a shake once a year. As long as it was still solid I rationalized putting its replacement off a little longer . . . and a little longer and a little longer.
The hot pipe is now 14 year old black iron in salt water and frankly looks like shi-shi. It is still solid but I'm not putting it off any longer. The new 316 stainless sched 80 hot pipe fabrication is complete (first picture), ready to install at the next opportunity. The second and third pictures are of the thread sealant I used. I'll report back after installation and some run time on how it worked out.