The one piece of gear you will never sell

I'll go with my amp, Deja Vu Audio amp, a push-pull EL34 amp putting out 17 watts per side. I love this amp especially since the Aerovox cap upgrade I did last year. It's reliable, sounds fantastic, and is cheap to retube just 4 EL34's 3 6sn7's and a rectifier tube. The same 3 6sn7's have been in there for about 5 years. Power tubes right now are Psvane but I also use Gold Lion KT-77's. A classic and a keeper.

I dream of one day having THE system where nothing needs replacing, but I suspect that really IS a dream. That said, I own a SMcAudio VRE-1 preamp that I consider the finest piece of equipment in my rig, and certainly the preamp I will likely keep for the rest of my days. I've some gear that I have owned longer (a Naim Nait II still sees some use but I am neither wed to it or motivated to sell it, which is not the same as wanting to keep it forever). The VRE-1 though, is just special and I long to feel the same way about other components in my rig. 

I think you might find that your ZeroStat will cease to emit ions. I have an old white one that is no longer effective.

My Vendetta phono stage will never leave my system - ever!

I'd be unlikely to divest myself of any of my three Classe DR3 VHC either.

Without a doubt my Sansui AU-111! I have owned and collected audio gear for years now and have owned Scott, marantz, other sansui amplifiers, conrad johnson, rogue audio, and many other audio gear, which I admired each in their own way, but if I had to narrow my collection to only one amplifier, it would be the Sansui AU-111. Nothing I have ever owned ever bested this amplifer, vintage or new. And for this reason, I will never part with it!