[mocko]

That's absolutely right but boilers aren't the only thing to wear out. With so many moving metal parts, despite an automated lubrication system delivering oil to most of the surfaces even the best designs of steam loco will shake themselves to bits before long. The regular expansion/contraction cycles as it's warmed up for work and cools down after also put a lot of stress on the metal.

Sixty years ago refurbs would be much of the work going on at any large railway works - taking engines apart, stripping them down to the chassis and reassembling almost a new one in their place. The ingenuity today's preservationists demonstrate in doing this without any of the facilities of a plant is truly a thing to behold.

(Source: some of my family restore steam engines. I once tried to drive one and I was terrible.)

[Animats]

> Sixty years ago refurbs would be much of the work going on at any large railway works - taking engines apart, stripping them down to the chassis and reassembling almost a new one in their place.

Here's the process.[1] This had to be done every 120,000 miles or so, which is every 1-2 years. On top of that, there's a few hours a day of routine daily maintenance.[2]

[1] https://www.youtube.com/watch?v=nZ3AN-kd66g