Anyone have this kind of problem with their amp?

I own a Classe CAP-101 integrated amp that I bought used about 10+ years ago.  Recently, it's developed a problem where the right output channel doesn't operate.  Sometimes, the amp works just fine.  But at other times, the right channel won't operate when I power up.  At still other times, there's no issue when I power up, but the right channel will stop working after a variable period of time, sometimes ten minutes and sometimes thirty or even more.  Occasionally but not frequently, after the channel has stopped working, it will resume working after a while, continue to work for a time but then may revert to not working.  When the channel stops working, turning the amp off and restarting it, and/or unplugging and replugging it, does not restore operability.  I've checked and re-checked my connections (bare wire) without any effect  

It's not my other equipment, because I've inserted another integrated without any issue.

I've taken it to a repair shop but the tech couldn't replicate the problem, so he couldn't diagnose it.

In the past, when I've contacted Classe customer support by email about a previous issue or with a question, I've never even gotten a reply.

Any thoughts/advice?  Thanks in advance.

Thanks to everyone for taking the time to reply.

Bsamooa, special thanks for your detailed questions and suggestions.  To respond briefly:  (1) there's no noise (e.g., boom or scratch) at sound cut out; (2) after sound cut out, no hum or hiss from the quiet channel; (3) I haven't tried listening after sound cut out to both speakers without music playing.

Bsamooa and noromance, I'm going to show your post to the repair tech.  He said he couldn't duplicate the problem so he couldn't diagnose it, but perhaps your post will give him some ideas.  If not, I'll bring the amp home, put it back into the system and when (and if) it fails again, I'll come back here and see what can be tried.
You sure there isn't an overheating issue? Radiator? Stuck on tight shelf etc?
Thanks, noromance,

Ever since I've owned it, I've had the amp on a wood shelf nowhere near a heat vent, with 3-4 inches of open space around the amp's top and sides.  The top (which has vents and which I've always kept clear) has always gotten warm to the touch during extensive use.  Consequently, I don't think it's an overheating issue.  
Not familiar with this unit, but looking at photos posted on this unit, does the design incorporate output relays ? The problem described, ime, sounds like this might be the issue, as relays have a notorious history of failing. Or an output current limiter circuit. Of course, it would need to happen during a test bench check, as experienced. Possibly, a weak solder joint, as well. Just some thoughts.
Does your amp have a relay based DC protection circuit ?  It may be falsely kicking in & latching ?