It is not a matter of what is drifting on the Sony monitors.

The use I2C control for the G2 voltage. If either the video process ic
that also does the G2 fails (which it does) or the eeprom gets
corrupted or fails (which they do), there is no way to actually
troubleshoot and fix it without the Sony DAS alignment software for the
unit.

With the alignment software it is possible to find out what the G2
value is in the eeprom and see if it can be changed. If it can be
changed then you know the failure is in the CXA video ic.

The usual failure mode is the eeprom will fail completely. Totally
black picture due to no G2 voltage. Eeprom will become corrupt, either
full G2 voltage or no G2 voltage. Video ic will fail, OSD will be ok,
almost always full G2 voltage and over bright.

The design and high failure basically requires that you are a Sony
authorized servicer for these in order to see enough of them to warrant
the cost of all the different alignment jigs and software versions for
each monitor line.