Hi,
More Update:
I replaced every one of those 2200/6.3V with new Nichicon 2200uf 10V
105 deg. caps (verified good by testing them), but that did not fix the problem. The symptoms are exactly the same as I described in my original post. Note: I also replaced some other caps that had higher than normal ESR (eg. 220uf 16V caps).Note: I measured in circuit the +5V and +12V voltage sources, and both were "clean" (scoped) and at the proper level.
Without a schematic, there isn't much more I can do. I have decided to abandon this repair attempt.
John