Monitor the main +/- DC rails for changes/imbalance. Monitor the voltage
over any zener diodes associated with the protection circuitry.

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Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list onhttp://home.graffiti.net/diverse:graffiti.net/

Could the idling current being horridly off be a possible cause?

I managed to obtain the service manual and was able to measure voltage
for the idling current.

According to the service manual, voltage should be at 7.5mV with a
tolerance of +/- 1.5mV. Left channel measured in at around 7.0 mV,
but the right channel was measured at over 30.0 mV.