Your Forever Pieces? What and Why?

McIntosh MC275.  (Although I've learned in life to "Never say never!"

I have a MFA Magus B bought in 94. Have upgraded it twice. I use it only for the phonostage now. 
Shout out to Sota turntables. Had a Satelite from 91 to 2005 and traded it for a Nova. Never will let it go. 
Also, have a Koetsu Rosewood from 86. 

My Sota Sappire, purchased used in 1987.   It's still amazing!
And my beloved B&W 801-series2's.  
I've tried many times to replace them, and i keep coming back to them. I've upgraded all of the crossover capacitors over the years, and re-oriented the inductors to reduce crosstalk.  My next upgrade is to consolidate the bi-wire terminals with one set of better binding posts.  I have tried many times to bi-wire them, and they always sound phasey and weird when i do.  So I'm converting them to just one good connection!    

The oldest piece I still own is a Stax SR-40/SRD-4 set that I got in the '70s. I have upgraded to a SRX Mk 3/ SRM-T1S(pretty vintage, themselves); but I still plug the SR-40s in to the T1S from time to time. They have something in their sound that I will always love. The SRD-4 is in my small system so I can use the SR-40s there, too... In my 1991 Nakamichi Receiver 2.

B&W 801, purchased in 1976. When they were gifted they sounded terrible, flat. I understand B&W designed them to be purposed as studio monitors. Fortuitously, I learned of a company, North Creek, that made crossovers (40 lbs of copper, each!) specifically to overcome the speaker’s shortcomings. After installing the crossovers they became extraordinary. I pretty much use them everyday in my second system.