Nad M3 non repairable

Just sell it on Ebay as not working, as-is.  Somebody will buy it.  Then they will tell you they want their money back because it's not working.  
I do think an amplifier should last more than 10 years, but you're lucky to get that out of a car and people accept it as part of life.  

@chayro 
When you sell on eBay "as is for parts only"( category you select at time of listing) there are NO returns allowed if it is not working. I guess if you sent something else entirely different to listing and description it may go badly but as long as fairly described you will have no comeback.

My 1992 Pontiac firebird convertible is still going strong.......

I owned NAD equipment for years, loved the sound, an M3/M4/M5 combo my last.  I thought it was great equipment, but not very reliable.  I had problems with the M3 & M5 when they were new.  The M5 kept losing it's programming, had to have that repaired multiple times.
Too bad the parts for the M3 are no longer available, great sounding unit!

@uberwaltz - That part about the returns was tongue in cheek.  I once sold my father's destroyed ESL tonearm which I described as "rusty junk" and the buyer told me the base was cracked!  He didn't want his money back though.  But that's why I'm sort of turned off by selling things mail order.  People want to buy used at half price and then expect new with warranty.  That's why I always try to sell local.  Come, inspect, listen and then make your decision.  

@chayro 
Sorry my bad...lol
I did not pick up on your inflection.

Yea selling can be a nightmare in today's age and it only gets worse as common sense is the least common of all senses!