If you read through the various threads, very few plate amps from the current (large) set of companies have had issues. Over the years, a few very small companies have failed after they received a bad set of amplifiers.
I have two replacement amps that so far have lasted 5 and 6 years, respectively. One replacement was used on a subwoofer whose amp lasted 11 years. I have six other subwoofers whose plate amps range from 5-20 years old that so far are giving me no problems.
In the late 1980s, I had two standalone subwoofer amps fail for a passive subwoofer. In the early 1990s, I had one subwoofer amp gradually fail (humming louder and louder after three years) that was on a low-level subwoofer (that I gave to a high school kid).