Thank you all for you responses and really helpful explanations, they made sense and they were spot on!
C68 had a bad joint and was in a pretty sorry state as you can see by the picture bellow:
The schematic says that this is 10nF capacitor but mine had printed 15nF and only measured 3nF.
In my junk of spare parts i was able to find a BU508A and a really, really old 7nF capacitor. I've tried them in circuit and i was able to get a nearly full horizontal deflection without blowing the transistor.
Eventually the yoke started arcing with the CRT after a few 2 minutes and the transistor failed, but this time i guess it happened because of the "not so up to spec" parts.
The thing is, i was
only getting horizontal deflection, not vertical deflection.
The IC responsible for vertical deflection is a TDA8351. On pin 7 i get a short to ground. I'm not really acquainted with these ICs but pin 7 measuring only 2 ohms to ground didn't made sense to me. Could this be also bad?
If that's the case, I didn't know that a horizontal deflection failure could cause also a problem in the vertical deflection area.
Also here is a picture of the S2055N as you required:
