Super helpful.
Without knowing if he's even tried to adjust the focus pot, there's no need to recap it yet. All he mentioned was adjusting the color pots, which has zero to do with focus.
If the screen is filthy, it could also contribute to the issues the OP mentioned.
Fastest way to figure out what monitor is in there is to post pictures. We don't know if it's a dedicated Neo cab or what it might have been converted from.