How long should components last?

Not normal. Not ok.

I think that about $5K put you in kind of middle ground. Above consumer audio, but in the mid-fi range. So the build quality can be good by typically not great... they use off the shelf subcomponents and stock replacements. For true high end products say starting above $10K... say $12K to $20 or above, build quality is much better, longevity is considered and the company will carry spare parts. Twenty years or more can be expected. They will last much longer, but to maintain their top sonic qualities, recapping after 20 years is a good thing. I had an Audio Research preamp that I bought in the late seventies and I used for over a decade, passed it on and it is still fully operational. I am sure many are still in use. 

Transports are often unreliable. They are mechanical... so it is not uncommon to have the transport go out on a player. But again, the higher end will likely last longer, they will test and carry extras. 

One thing you elude to is that while the performance of luxury German cars is legendary... yes they are. I drove on in Germany for a while often at speeds around 150 mph. But they are not that reliable, I don't think you have to wait five years for their reliability to go down. You want reliable, you buy Japanese. 

So, seems you have had some bad luck... but not tremendously surprising. Sorry. 

I expect a life 10-15 years or more on quality gear.   I can't even remember the last time I had a failure in 40 plus years in this hobby outside of a tube or a fuse.   Been extremely lucky, mostly tube gear the past 25 years....

The most reliable electronics, ime, tend to come out of Japan. When I buy expensive electronics, it will  almost always be Japanese.

When I buy cheap electronics (i.e. i don't care too much if it breaks), I'll buy it from the Euros/Chinese/Americans/etc.

Can't say I've ever had anything 'break down' on me within even 10 years. Were your CD transport and DAC from the same company?