Amp not enough power

Does electronics degrade and changes the quality/sound of the amp?

Yes. Capacitors tend to be the most common culprits, aside from tubes in tubed equipment. Electrolytic capacitors in the power supply circuits could affect power capability, as well as sound quality. Smaller capacitors elsewhere in the circuitry, especially if they are directly in the signal path, could affect sound quality.

However, if the only indication of a problem is the max power measurements you were provided with, I would not take any action until the tech answers the questions that I and Eldartford stated.

If you and the tech do conclude that the electrolytic capacitors are probably causing a reduction in power capability, and you decide to have them replaced, it would probably make sense to have as many other capacitors as practicable replaced at the same time.

More generally, concerning the ability of older equipment to work well, the following threads will make for interesting reading. The upshot is that the performance of older equipment is very hit or miss, with little predictability, but in the better cases older equipment can continue to work well for MUCH longer than might be expected.

http://forum.audiogon.com/cgi-bin/fr.pl?htech&1267845685

http://forum.audiogon.com/cgi-bin/fr.pl?ymisc&1274033569

Regards,
-- Al

Am I reading this right? You are within 5% of spec. If that is the case, what are you worried about?

Get more efficient speakers.

Thanks, everyone, especially Al. I had suspected about the power Caps to my Aragon amp. They are the direct voltage supply to both channel boards. I will try to locate the caps.
You can treasure a product and still keep it going unless something major breaks. I will certainly try to keep my Aragon in good working order.

400W is only 1.5% louder than 380W - don't worry. I would recap this amp for better bass control. I changed power supply caps once and that is what I noticed. Bass became shorter more dynamic and cleaner.

Older caps have higher ESR (internal resistance) because they dry out. This internal resistance will keep increasing progressively because of increased self heating (but it will take many years). Eventually it will become so high that full power test, that you did, might trigger thermal runaway (temperature increases ESR that increases temperature by self heating even further and so on) and cap might blow up its mechanical fuse (rubber plug) or explode.

Electrolytic caps are the only components that age and are worth replacing if you like the amp. There is a good chance that you might be able to find today much better capacitors (lower ESR) than original.