Got curious after getting home and looking closer at those photos. it really is leaking only at the joints. So what did the old-timers do in the 50's to seal those connections and could that seal be the culprit?
Found this:
https://www.quora.com/How-were-the-o...ey-be-replaced
https://www.youtube.com/watch?v=RnCwChSBqFA
The joint is not a threaded connection!
It's a slip fit and the plumber packs in a fiber called Oakum, then seals it up with molten lead. A nearly lost trade today. To me this seems like a "cut it out and replace it" situation.