In the FWIW category, just today I put some miles on a '70s vintage Lionel Alco that has plastic gears. The engine has so much use that its pilot is broken and the shell is worn. It runs smooth and steady still at 50 years of age or so and pulls a reasonable length train as easily as if there were no cars behind it.
Will this engine perform as well in 50 years? Who knows? I just know that my childhood Alco--similarly worn but whose pilot is not broken--runs better and more reliably than all of my digital era, TMCC or Legacy engines.
