Target Systems (TSI) Laser diameter gauge question

These gauges are failing due to "Low DAC values". These are analog laser gauges that rely on the intensity of the light falling on a detector. I take the error as being caused by the gradual reduction in intensity of the light source - either by dirt, optical mis-alignment, or a gradual degradation of the light source itself.

Has anyone had any luck repairing these antique gauges? Our repair facility - who shall remain nameless - doesn't want to mess with them anymore.