Amp longevity, if well taken care of --the risks of purchasing used equip.

I wouldn’t worry about it. I’m using the same ICE module but not the Bel Canto case. Still works great.

mk1 is basically just the module. You can find D-Sonic amps using that module for 1/2 the price.

The replacement module can be bought here $400:

https://www.parts-express.com/ICEpower-1000ASP-Class-D-Audio-Amplifier-with-Power-Supply-Module-1-x-1000W-326-206?quantity=1

I have enjoyed most of my gear for years, to decades. I have also bought most of my gear used. I particularly had issues with a YBA CD player, which went for repairs twice in the 20 years I owned it. Rubber belts. To be expected. 
I had an ongoing issue with an AR LS15 preamp. The main problem was mostly an unscrupulous dealer. I paid to have a problem fixed, and they insisted on installing new tubes. A month later, same problem. I took the unit to a 2nd shop for repairs, and to my total surprise the 2nd shop told me the pre amp was totally full of dust inside ( obviously had not be cleaned by the first shop ) and that the tubes that were installed were total garbage, with a crazy amount of background noise. I wasn't sure who to believe.  I am still using that AR LS15 daily with the 2nd set of tubes installed, still sounds great, likely 10 years later. The first dealer scammed me.  The first dealer has since gone out of business. 
My take away is this, take it to a repair depot, not the dealer. Quality does matter. There are bad designs out there. If a circuit board is bad, there is a good chance it can not be repaired.  If it is a bad component, that can be sourced and replaced, in a well designed piece of gear, go for it.

I purchased my Yamaha RZ-Z9 new in 2003 and it has over 35,000 hours and still plays just like new.

...Maybe the fan is a bit louder.  Never been serviced.

My amp is from 1977, it has worked beautifully. I did do a full referb 2 years ago, it does sound much better after, but it has never let me down. 

If something is going to fail, it will fail, doesn't matter if it's a week old or several decades. 

As a 20 something I bought an Adcom preamp and amp for $300! Adcom was in New Brunswick NJ close to where I lived I took it to them and while I waited went through the entire amp and pre making changes as they went and gave it back to me free of charge!!