Power Amplifier Longevity

Hi All, 
I am venturing into the separate component world and was wondering how long a good power amp typically lasts.  I may have access to some older Lexicon CX and LX series amplifiers.  However, since they are discontinued and nearly 20 years old from what I understand, should I be concerned with how much longer they will last?  If they do need servicing, is this something that is available at a reasonable cost?  Or should I invest in newer equipment?

Budget is a concern for me which is why I am interested in these older (higher quality) amps at a reduced price versus spending the same amount on something newer, but lower quality.

At this time, I have a Marantz AV8802A and Vienna Acoustics speakers. 
Main L/R - Mozart Grand
Center - Maestro Grand
4 Surrounds - Waltz Grand

I thank you in advance for any advice provided on this subject.

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I have a pair of monoblock 125 w. Class A/B tube amps with humungous power (electrolytic) storage caps.  They are several decades old and are fully exposed to the air.  The adjacent transformers run so cool that I can nearly wrap my hand around them after hours of use.  

Contrariwise, I have an EAR 890 that after 20 minutes, is nearly boiling hot and touching the transformers can melt one's skin off.  It's a Class A amp with small tubes sealed in the circuit board upside down.   This amp may need new caps in the future.

My prior Audio Research SP14 had a burned out resistor on the center of the circuit board after only 5 years of heavy use.

My McIntosh MC30s still run fine with original caps.  It runs hot as does my modified Dynaco ST70 (new larger storage caps).  

Two Yamaha CR620 receivers began to hum and caps were replaced after 35 years of use for video.

So, some caps last many decades and some probably will do to their high quality and low heat exposure.   Other caps and resistors can burn out rather quickly due to internal circuit board heat.
If you do get an older amp be sure you can find service manuals and schematics for it. Most everything is repairable with some exceptions. But it is much harder without a schematic.