Yes it will in 99% of cases be the EHT, could be as simple as moisture in the air, adding to dust creates mud

& the high voltage starts to leak, if your game you could unplug it, take the cover off &
carefully vaccume it, this has fixed that type of problem in many CRT monitors I've had to repair.
Edit: Sometimes you can hear the leak as a hiss, turning the lights out you may see the leak, then shine a torch on the spot for identification, this would have to be done with the cover off, but beware of HIGH VOLTAGES!!