What, in your system, have you owned the longest?

Silverline Sonatina speakers. Bought new in 2003.

I was going to say the speakers, but the reality is the Furman 15 A elite something something is definitely what has lasted the longest.

Gik 244 Panels and my Porter Port.  At one point, about 5 years ago, I sold off my entire set up yet still kept these, lol

Ariston RD11S bought new in 1977! Still in use! It has had a variety of arms - and cartridges - on it. In order: SME 1009IMP, JH Formula 4, Keith Monks, Lustre GST-1 and at present a Grace 707 with a Denon 103. Record mat is the Hiraoka Diskmat SE22 I bought in 1977 at Harvey Sound (NYC, 48th Street) for $20! Still an amazingly fine sounding TT! The RD11 and RD11S are the Scottish cousins to the Linn Sondek. Actually, the progenitors! Ariston made the early LP12's before Ivor Tiefenbrun set up his own factory. He just copied the RD11 and marketed it as his own original design! Hamish Robertson was the owner/designer of Ariston who got HIS inspiration from the earlier - and wildly successful - Acoustic Research AR TT from 1961.

Burmester 961 speakers in 1996.
Michélle