Thanks to everyone for their help!
Stereo5, I'm going to try contacting Classe again. Who knows, maybe I'll get a response this time.
The local repair shop I went to is Audio Specialties here in Portland; the owner, Doug, is well-respected. I don't know specifically what he did, but I would trust him to have done a thorough inspection. Still, I may ask him about identifying possible cold solder joint issues.
Bigkidz, you're very generous to offer to look at it. But I'm in Portland, Oregon, and I think the shipping costs alone would be prohibitive relative to the probably fair market value of the amp, which I think is in the $400-500 range. When repair costs are factored in, I'd have that same consideration if Classe wants me to ship it to them.
Skyscraper and EBM, I feel ya.
The amp is back in my system now, working without problem. But tick, tick, tick.....
One final thought: If Classe knew that boards were defective, even it discovered the fact after manufacture, should it have an obligation to repair/replace the boards without charge? Now, it's been around 20 years (or more) since the amp was measured, so Classe probably doesn't have any legal obligation (statutes of limitation and ultimate repose and all that), but how about a moral or ethical obligation? If Classe responds, I'll ask, but I'm not hopeful.
Again, thanks to all! A great community here!