The amp in question is the Nelson Pass designed Adcom GFA-555, cira 1984-1995
As of today there are 20 listed for sale on ebay, all stated as in good working condition.
None are currently listed as inoperative or for parts only.
After 21-32 years in service that's says something about their "inefficient cooling" design.

Once again, if you pack as many components in a single 17" wide chassis as possible with little
room for circulation the heat and time will eventually take it's vengeance.
Even given the belief that all modern apps sound the same, if you purchase amps on the highest watts per dollar path, somethings gotta give. First on that list will be life expectancy.
Ciao,