"Thomas G. Marshall" said:

Maybe I should ask this a different way that doesn't put you both at each
other's throats (regardless who's right).

No prob, we're just doing our daily dance.
Afterwards we kiss it off and have a beer together :-)

If I go and open the thing up.... Besides seeing a lot of dust (could that
cause this?), what should I look for besides loose components and burn
marks?

When you see obvious things like loose or burned components or
tracks, the fix seems easy. That's unlikely though, since you implied
the receiver works well most of the time.
However, I think you'd benefit from resoldering at least the
power/driver transistors/ICs and large resistors in the amp stage.
Check the entire PCB for suspicious solder joints (kind of hard to
explain, but once you know what to look for, it's really easy).
If there are any mechanical switches in the signal path, such as input
selectors, speaker selectors or speaker relays, spray them with
contact cleaner and push/turn them a few times around.

If that doesn't help, it will need a more thorough checkup, and it's
up to you if the receiver is worth it.

--
Sander de Waal
" SOA of a KT88? Sufficient. "