system
Given the following post, respond as if you're commenting on Reddit:
human
[Wh40k] What system Imperium of Man has in place to solve military equipment failures, replacement parts?

All machines and technology will and does eventually break down. The causes of equipment failure are too numerous to be listed, but the point of this thread is not to talk about reason why, rather the Imperium of Man's response to it.

So, imagine this scenario: Bob and his fellows tankers are driving along one day when a wheel from their tank falls off. How do Bob and his fellow IoM tankers fix it?
gpt
First, if Bob or his tankers touch it and an Adeptus Mechanicus designee sees them doing it in any way improperly (eg pretty much any way a guardsman has ever fixed anything according to the Mechanicus), they're going to die. Either figuratively due to chiding and lectures on the fragility of the machine and its spirit spirit or in the most egregious cases literally torn limb from limb by an.. well not enraged because the Adept might not have the emotion portion of his brain anymore, but certainly you'd understand the feeling as displeasure. This is unlikely to happen on any average local model or Leman Russ and probably extremely likely on a Baneblade that has a dedicated initiate of the AM along exactly to fix it.

If there are no AM gearheads around because they're all dead or because they're busy dealing with other more important matters like how best to activate some incredibly dangerous archeotech, Bob and crew fix their tank like any other tanker from any other century that has ever had tanks. If they do it under fire, some of them probably die. Or all of them. If they do it on the field during a march, they fall in and catch up after they're done as best they can. The spare parts are either obtained from a store of spares carried on the tank, from a depot, scavenged from a dead tank, or jury rigged from anything available at hand. The spares are made in various places and transported along with the rest of the unit and as needed or available like any logistics chain.

The most important difference is that the tank isn't fixed until someone has said a prayer and offered incense to the Machine Spirit. That is not a figure of speech. If you don't appease the Spirit, the tank may fail in the middle of battle.