I've used deoxit spray to clean pots etc on a couple of ageing amps including my current Kenwood 3020SE, which suffered with a crackly volume pot etc. Like you I had to fiddle around to get the selector switch to stay in same the same position between two different inputs or the sound would drop off in the right channel. An all round sonic improvement after cleaning, including the fuller sound you mention, which I think is because the amp wasn't performing 100% not only the right channel but the left as well, even when I had the input switch precariously positioned.
I cleaned my amp approx 18 months ago and it's still going strong.
