Follow up:
After about 2h45min and turning up both the intensity and readout, the display and readout were still in the sharpest setting.
Adjusting focus and/or astig would make the screen less focussed.....
I would suggest to (before and after) check all relevant voltages on the CRT.
Geometry, edge focus, y-axis alignment, and the components around Q4422, Q4402 and Q4403.
Maybe a cold solder joint in that area?
Un saludo,
Leo
satbeginner