1995 TMCC 2380 GP9
1995 TMCC SD-50
1996 TMCC F3 A-B
2000 TMCC Century Club 773 Hudson
etc..etc.. like a Phantom set, a couple more GPs.... then current day stuff:
Legacy Daylight Cab Forward
My TMCC base and handheld are my originals from 1995.
Everything works, whether 21 years old or 2 years old.
Sure, I throw traction tires now and then, and need to do some smoke tube (blow down the stack) maintenance now and then.
One thing I do yearly is open them up and make sure the pc boards and traces are not oxidized, wires not pinched, and all boards seated well.
My experience has been similar with my three MTH rail-king PS2 that I started buying in 2004.
Besides all that: I am not worried if my trains will run 50 years from now. I most likely won't be here.