Dang, this'n is a brain buster for sure.
Nothing about the symptoms make any sense unless... and this is purely a shot in the dark:
Those replacement caps for C4A and C4B. Sometimes foreign-sourced electrolytics have the arrow pointing to the negative end of the cap. Intuitively, you'd think the arrow should point to the positive end, and you end up installing the cap backwards. Is there any chance that coulda happened?
Another shot in the dark.. are you using a digital meter to take voltage readings? If so, is there any chance you could use an analog meter to re-take the readings? I would never trust a digital meter on anything other than pure DC or pure sine wave AC.