I have a few pieces in my system that qualify, except (as you specify in your post), I haven’t replaced them or removed them from my system. Occasionally I take them in to have some of the internals upgraded or repaired, but they will always be an integral part of my system.
So the pieces I can’t let go of are my musical instruments. My string bass, my electric bass (which turned 50 two years ago), and a couple of my guitars. I haven’t played them in over 35 years, but they were so prominent in my life that I’ll never sell them.