Thing is, most of this sort of thing exists, to a greater or lesser extent, with current ships and aircraft.
You'll always, always still have a basic workshop - i.e. drill, tap, files, etc - because you can't rely on your CAD/CAM machine - as suggested, above, what happens if either it or the power supply are what's broken? Under normal circumstances, however, everything can get simpler and easier.
Most (seagoing) ships carry a small workshop and ingots as well as a (small) stock of prefabricated common items. The more efficient the fabricators, the less 'on-spec' stock material you need. The more complex a system, the less predictable your needs, so the less useful rooms of spares are, anyway.
Adaptible component spares are something manufacturers like - because a manufacturer likes you replacing a plug and play module and will make it as easy as possible for you to do just that (think USB, self-loading drivers, etc, today) and/or make the turnaround time at his service facilities as fast as possible. He doesn't like you being able to fix damaged components because he doesn't get money from that. He may repair the component he pulled and put it back into stock, but he'll do that in his own time when you're not there tapping your feet with a busted ship/car. This is, for example, why the concept of a 'panel beater' has almost disappeared today in car service shops.
Test sets are the same. Even if the entire thing isn't common some have adaptor kits to fit any system they might need to interact with. Something the size of a mobile phone today has significantly more processing power than the entire US Air Force Maintenance Command at the height of the Cold War. Go to TL12, and imagine how much information you can have in even an 'inert' component - essentially disposable swipecards for buildings or tags for products in shops now often use an RFID chip - if engineering components include these you can pull off their maintenance history with a self-powered handset even if there's no power to that compartment.
Not to mention a hand computer with Expert Engineer; large friendly letters saying "Keep Calm And Hit The Master Reset Switch" can turn anyone into a passable technician. At least outside an emergency...