My Onkyo 875 (UK) is 3.5 years old (bought Sept 2008) and hasnt put a foot wrong.
I've been watching posts about how hot they get since before I bought it, so stuck a 200mm fan on top drawing air out from day 1.
It hardly even gets warm.
It is on about 16 hours per day, almost every day, often left on overnight by accident.
Its Bi amped to a set of home built speakers (200W 91dB and front+surrounds) and gets some rough punishment
An incredible amp.
Granted this an experience of one amp, but perhaps as already pointed out, a fan is all that most of the failed units needed?
I've seen a few posts claiming their Onkyos died with a fan on, so take this with a pinch of salt.
But also question whether those amps were allowed to get very hot at any time.
By the law of averages, some machines with fans on will die anyway...
Another thing to consider is that my amp isnt switched on and off a lot.
Because they run so hot without a fan, the heat cycling damage to components and electrical joints is much greater.
So a combination of no fan and switching on/off a lot could be a major cause of the failures, although I think just running with no fan is bad enough with the temps reported by users and reviewers.
No doubt this is made worse if the amp is used hard a lot.
This isnt a dig btw.
I wont buy Onkyo again after reading about their customer service.