I still have numerous maplin kits from the 1980s all audio kits assembled that still work,I built an amplifier with bass and treble controls,mic inputs,15 tad 2030 amplifier,power supply etc and all of it still works perfect.
After about 28 years of me nuilding it all into a case etc, it still works perfect and sounds amazing
I even still have some original circuit diagrams, pcb layouts etc of various Mapllin audi kits