Just for completeness:

As noted, after much effort, I did get the rod out. Next time, I'll get
an impact wrench. I put a new (aluminum) rod in. I flushed the tank
several times, including 2x with vinegar. One thing I found is that it
flushes much more 'powerfully' if I remove the draincock.

.... And, it's running, no leaks so far. We'll see how it goes.

Thanks to all who replied.

George