You must have a much better mechanic than usual. Most of the ones I've worked with tend to make a quick guess at what's broken, and just replace it. I call it "throwing parts at the problem" when it goes badly.

Though in defense, most of them are good enough to guess right 90% of the time. And mechanics generally get paid by the task, not hour. Replacing the probably misbehaving X pays. Spending an extra half an hour making sure that X really is broken and replacement is the best solution doesn't pay. So they just replace the X and hope for the best, and then replace something else if it didn't work.

Replacing a standardized part in a mechanism that is built entirely from such parts is quite different, though. You don't have to worry about breaking something - and that is entirely by design. This kind of thing is what makes the logistics behind our civilization scale so well.

That we do have to worry about breaking something in the software industry field, just tells us how far we've yet to go.

Agreed; it's a blessing. I'm actually keeping my brand of car as long as my mechanic retires, and I have 2 brands that I won't ever touch again due to bad experiences with contract garages.