Comment by erickhill
When I was in the Air Force in the early 1990s, we still used KC-135 "flying gas stations" that had been built during the cold war in the 1950s. While expensive to maintain they were far less expensive to fix than buying new and starting from scratch. With regular full maintenance checks in the hangars (wash them, inspect them with dental picks and flashlights, replace broken parts, etc.) we kept those planes in service and mission ready for decades.
There was an entire supply chain of every single part ready to go, with technical manuals for every maintenance task you can imagine. If we couldn't fix something, it would go to the jet lab or machinists or whatever.
The system in place is mind bogglingly good.
/edited for a typo.
Hell, the KC-46 only entered service a few years ago and they’re talking about extending the KC-135’s service life into the 2030s.