Bob,
Thanks for the advice - I sort of came up with something like this out of weariness. Switched between two penetrating oil (I had run out of Blaster and had no car) between Marine Pal and (ugh) Liquid Wrench. Let it sit; tap-tap-tap - warmed lgihtly with a quick use of propane torch. Repeated. When the assembly startd to move a little, I reapplied the pentrating oil, put the nut back on and tightened the assembly. Figured it work the corrosion lose. Repeated. Was about to give up and let it all sit overnight - it does help - when it all cmae loose. Was lightly corroded, but in that tight space, that was enough.

Between my experiments - mild heating did help - and your advice, I've now have a game plan for the future when I get stuck again. I would never have thought of seeking a loaner tool! I have enough one-time tools in the crib already (I am sure you know waht I mean.)

Thanks for your support and advice.

Brian