The firmware update solved the problem!
After this more than a year of trying to find the problem with my 20 year old 500/4.5L lens with my 5dII body wherein it would not focus in the critical zone and would not accept microfocus adjustment to fix the problem of being slightly out-of-focus 90% of the time, the firmware update did it.
I had the lens into a Canon authorized repair shop and they had no problems with the lens and their test bodies. As a follow-up to the inspection they did I talked to the tech who said that there was a known, rare condition when a body and lens simply did not work together. This led me to query this website and I got a really good link to info on how the Canon AF system works, thanks to Glenn NK, which led me to follow-up on my speculation that perhaps a firmware update might help - and it did. Check out http://www.bobatkins.com/smf/index.php/topic,995.0.html
for details and various other threads under my name for the gory and extensive details.
Please expose this info widely to try to help any other Canon users who have suffered as I have trying to solve a problem for which Canon is of no use, whatsoever.