I would just continue to use the monitor if you're happy to do so. If you feel the symptoms have worsen/ seeking peace of mind/ then perhaps highlight what's been mentioned in this thread to those TV repair people.
I asked about the resolution change to rule out and narrow the possibilities.
I understand your concerned to preserve and maintain the life span, as many others are, of their beloved CRTs. You mentioned yours is primarily for games perhaps consider using a portable TV via RGB SCART.
Foresight:
I appreciate some users like their uniformity with Amigas and Commodore/Philips/Daewoo monitors as they are of a period and aesthetically in keeping; but technically it is afterall TV technology (not at its best) and considering the high prices the monies would be better invested in perhaps a nice mid 90s 14inch Sony Trinitron FD.
You can pick these up for almost nothing because of the flat-panel craze.
The technology, picture quality, so forth is far superior to any of the C=/Philips/Daewoo tubes and any cash you'd save could buy you a couple of extra Amiga games ;)
Skippy.

