Amps from the 1980's -- What gear holds up sonically? Reliably?

Agree strongly with the Electron Kinetics Amps. All of the Eagle 2 series power amps are stable down to 2 ohms. They became the building platform for all of the mono amps that followed.
I managed to purchase a pair of 11 prime mono blocks recently and will never look back!
I purchased a 7a dual mono amp from John Iverson and later he upgraded it to a 7b (only 22 exist) which I still have.
Used to own Thresholds, Accuphase, and briefly Phase Linear. None compared to EKSC Eagle, especially with dynamic loudspeakers.
The BEL (Brown Electronic Labs) were peerless and remain so when driven as mono blocks for Electrostatic Loudspeakers, especially Dayton Wright's.

I still have the Krell KSA 250 that I spoke of above. I had it updated to a 250S, sold it bought a 700C, sold it and ended up with the 250 again after the owner died. I have been using it quite a bit although I have a pair of Citation IIs running in balanced mono, it still sounds great.
I also have a Yamaha CA 2010 that sounds super and a Mcintosh MA 6100, a Bryston 3B, Transcendence 400, Belles 1, a pair of Audionics and various other Yamaha receivers. There may be others.

Boulder amplifiers.
Still very much in love with the 500  and don't see any need to replace or update. Absolutely amazing to this day.
As for reliability I expect this will outlive me, easily (no, I'm not THAT old),  and still sound spectacular.More info here for those interested: http://www.stereophile.com/solidpoweramps/886boulder/index.html

Count me in as another Adcom affectionado.  My introduction into the world of separates started back in the late 70s, when I bought a Sansui QSD-1 four channel unit and started using separate amps for both the front and rear channels and a little later on, I added biamping to the mix and added a third amp.
My first set of dedicated amps were a matched set of three Heathkit 125w/ch amps which I built over the course of one, long summer.  The Heath amps lasted about six years and then one of the channels went out on me.  Looking around for a replacement, I wandered into a stereo store and picked up an Adcom 545 - only 100w/ch but i figured it would be OK for the subwooferes.
As soon as I hooked it up I was aware this little Adcom was way better than my more powerful Heaths.  So much better that I immediately started collecting Adcoms.  
My next Adcom was a 555 which I put into place as my front channel amp. By this time I was using Magnepan 1a speakers for both the front and rear and the 555 proved to be a wonderful partner.  A audio-sales friend of mine told me that if I thought the 555 matched well with Maggies, I should try the 5500.  So I did.
The MOSFET design by Nelson Pass turned out to be a match made in heaven with the Maggies.  It didn't take long for the second 5500 to come into my system.
25 years later, my three Adcoms still form the backbone of my system.  I still have the same pair of subwoofers but the Maggies have been upgraded to 1.7s, front and rear.  All along I have had a pair of McIntosh C-20 preamps, each placed just before the 5500s to provide final balance and volume control plus add that wonderful tube sound.  The tube preamps work so well with the MOSFET design, and the resulting sound that comes out of my Maggies makes every listening sesion "a little slice of heaven".  Hopefully, I will never have to change.
Now, I don't mean to suggest I haven't done anything to help these amps.  Both of the 5500s have been in for service a couple of times and about five years ago I took them in and had the caps upgraded. This summer they are going back in and I'll have the power supplies looked at.  But even if the power supply is upgraded my maintenance/upgrade cost over these 25+ years will average out to about $35 a year.  For that expense (after all these years) I get a fantastic soundstage, a warm, liquid sound, and a noise floor so low that as a song winds down and it gets to the few seconds between songs, you'd swear that nothing was even turned on.
On the other hand (except for a replacement off/on switch), the poor, little 555 has had absolutely no service performed on it since the day I bought it.  Since the 555 has more bass than the 5500s it has been powering my subwoofers whithout a flaw for 25+ years. 
Thank you Nelson Pass !!!

Reading one post they were known as flame throwers that is because of people pushing them too overload like a junky the more you turned them up the better they sounded until blow up time if kept under the o dB point no problem. I've got two 400's that have never been touched but the ones heavily used will need the electrolytes on the circuit boards as they  definitely need to be replaced to last another 30 years  Even with the rebuild they still would be a lot cheaper than some new ones