What could cause this amp to fail?

Hi Everyone,
Apologies if this is the wrong forum for this question. I just got into serious speakers (been into headphones most of my life). I picked up a pair of Thiel CS1.5’s that have blown me away. Anyways, I also bought a used Perreaux EX-120 (circa 1994 MOSFET Class AB 100wpc) Integrated amp on ebay for pretty cheap (seller had no feedback and I decided to take a chance) which is the subject of this question.

For the first few days after plugging it in it sounded great: warm, smooth, powerful until on around the fifth day, I noticed the sound cut from the amp and what sounded like a click. I powered it down and let it rest. The next day I heard the same thing but it started to happen more and more frequently. It would start about a minute after starting to play music and then quickly increase to the point where it would be clicking and cutting out multiple times per second (it doesn’t happen if no signal is running through). There was also a noticeable clicking coming from within the amp itself. The problem now starts happening immediately after putting signal through it and doesn’t stop.

I took it to a local audio repair who thought it was a relay issue but was unable to fix it after several tries. He referred me to another repair shop who has now told me that 8 Mosfets in the amp are blown and the input selector has ’aged out’. To repair it would cost about $450 dollars as he would have to replace many components in the amp and that it would end up as a just a power amp since the selector is a custom component that Perreaux doesn’t sell anymore.

I’m trying to get my money back from the seller, but he’s pretty much refusing saying that this is impossible and suggesting that I must have overloaded it since it worked when he sent it out. One thing to note is that I have carpet (not deep, quite short) and the binding posts on the Thiels are at the very bottom where I imagine it’s possible that the carpet could come into contact with the connectors. I have 2 other amplifiers (an entry level Cambridge Integrated and a B&K receiver which is a MOSFET design) and neither have had this issue.

My question is: could static electricity or contact between the carpet and the binding posts/cable connectors cause the amp to fail? If so, how come it took 4-5 days? If not, what is the possibility that it is my fault?
I will never forget when I was listening to a pair of $30K Sonus Faber speakers driven by $35K Mac monoblocks.  I being a wood worker was fascinated by the wood work on the speakers.  I walked up to them to look at the inlays and veneers.  My foot came close or contacted some quite nice speaker cables.  SOUND STOPPED.  The static from my foot kicked out the protectors on the amps.  I thought for a second.  Oh no I just blew up a system way over my head.  Dealer unplugged the amps and away we went.  So static is an issue. 

This is why i always buy new.  Nothing like having a 5 year warranty.  I am sure there are reasons why people sell of their equipment. 
I am sure there are reasons why people sell of their equipment.
Yeah, it's called upgrading. You've never sold anything?
There probably is a junction transistor phase splitter circuit driving all of the final output MOSFETS . If this develops heat sensitivity it could put a DC potential at the speaker terminals. The relay circuit is there to detect this DC and shut down the amplifier before it blows your speakers out. You need a repair person who understand how high power amplifiers function. Youtube has a number of videos posted by people who really understands this stuff and could probably help you.
Thank you all for your replies, this have been very enlightening. As I mentioned earlier, I'm new to the speaker world and know little about amp pairings, etc.

I’ve decided to not go through with the repair since given what @8th-note, @mlieber507 and some others have said. It seems likely that the amp was working ’fine’ for its age but failed due to the stress place on it by the speakers. I may end up repairing it in the future but certainly not with the current repair guy since some of what he said doesn’t seem to make any sense. In the meantime, I will be eyeing an Adcom GFA 555 II.
Feel free to leave some more recommendations for amps that pair well with Thiels, integrated or otherwise.