How do I handle equipment breakdowns I can't figure out?

You can keep most of your equipment running, and that is no small thing. What stops you now is the rare, tangled breakdown, the one that does not match anything you have seen. That is the hardest tier of the work, and struggling there does not erase everything you already handle well. Complex breakdowns usually have more than one cause stacked together, which is why they resist a quick fix. The people who solve them work slowly and rule things out one at a time instead of guessing. They also lean on manuals, on other hands, and on the machine's own history. Next time one stumps you, stop guessing and write down what you have already ruled out. Bring that list to someone who has been at it longer. You will learn the tangled ones the same way you learned the rest, one hard job at a time.