When to know my amp/receiver needs to be maintenanced?

I heard that amplifiers can go bad after a while even under normal use, such as dry-out capacitors, wornout resistors, in-rush current damage and such expendable parts. From what I heard the highs of your speakers can start sounding dull and lacking bass, then eventually will sound worse until one day the thing just dies. I have a Technics SA-DA10N reciever(gold color!) that has been running above 100Hz all its life, a Technics SU-V8X that has been running 2 pairs of 4ohm American Acoustics in parallel full-range for our parties, and a Proton D1200 which I've only used for 100Hz and below and with a inrush current of about 9 amps. Can I "tell" if my amps are going out? Is high inrush current normal? The Technics receiver is about 3 years old, the other one is close to 24, and the Proton is about 16 years. They all sounds great right now and have extra fans for cooling that I added...

Yikes I don't know where you get this info - but a Solid State amp will more than likely just fail. Tubes wear out over time and you replace the tubes. Yes a capacitor can go but you should be fine for at least a decade.

Maintenance of an amplifier probably costs more than it would to replace it.

maintanace sometimes does cost more, but dont you notice that there is a group out there that always likes the old models?

Lets say someone really likes naim i-amps. This person swears the nait 3 is the best naim out there and the nait 5 is nowhere close. 2 options...buy used(which might break down just the same) or fix the old. You'll always have your crowd...maybe not a big one, but its there

I love my Proton D1200...sooooo much clean power...but right now its just sitting there cause I don't really know what to do with it...