Thanks DublinTrader,
Yes, I've Deoxed it a few years back. It did have a scratchy volume knob at one point. I may spray it again, but the left channel issue doesn't react to any knob turning, and seems to be a heat-related issue. The channel will often suddenly pop on after the unit's been running for about 20 minutes. Oddly, I can engage both channels with the spatial expander function, but I don't care for the effect.
I'll spray it in few days and report back if any improvement.