Replying to my own post, here.
I am happy to report that the big old 1/2" Plomb pebble 5449 (large letter Made in U S A version) is up and going like new.
First I soaked it in gasoline to get the worst gunk off--even before I opened it up. Then I put some light oil on it and let it set for a day. Then went at it with a soft brass brush. It cleaned up pretty well, showing the best patina I could expect.
Then I took it open and cleaned it properly. Could not find anything wrong with it. Greased it and reassembled, but it still would operate occasionally--and not properly. Finally it dawned on me that the selector switch was a little too floppy. It was sprung enough that it did not engage the pawls correctly. I corrected it with a small C-clamp.
After all those years, it works as well as ever.
BTW, the Plomb was on the Dollar Table. I paid as fast as I could. Then asked the seller why it was for sale at such a price. He said it had been for sale for nearly a year--with no takers. As he said, "Tools get heavy."
Just Wow!