Thank you Strat, I'll investigate. It looks like I have a new project/hobby on my handsExcept if it were a tube issue you'd have the same focus issue on the entire display area. So no.
If I look at the pictures it seems both lines are affected, but these aren't very good pictures. You have the screen in front of you, if you tell me the problem is only with the horizontal lines then you have your answer. The problem is either with the vertical dynamic focus section of the circuit on the D board, the +15V / -15V lines or the N board.
edit: ahaha, mistake.
Looking back at the schematics the vertical dynamic focus is a circuit actually separated from the vertical deflection. That kind of signal goes to the flyback.
I hope I can find quality spare parts such as capacitors or transistors if I decide to delve deeper into this.