Some manufacturers from olden days such as Audio Research and Mark Levinson (the brand name) still have active service departments. Recently, I used AR to fully refurbish an old SP-6B preamp. They did an excellent job. It will last as long as a new model would.
You can buy used equipment made by these manufacturers with the knowledge that repairs are available. You will have to pay a bit more, bit it will still be much less than the original price (keeping inflation in mind).
I have worked on tuners. Almost every one more than 10 years old will need a fresh tuning and calibration. This is a very specialized task. There are few people today that have the skills needed. I always keep this in mind when I buy a tuner. I have learned to do this tuning, but I an definitely not an expert. The DA-F20 is a bit difficult to do. I agree that it sounds very good. Sansui TU series was also very good.
It also helps to buy from reputable sources such as Audiogon, US and Canada AudioMart and HiFi Shark (for all listings). Sellers are motivated to be honest.
Happy Hunting!

