The situation
In my Level 2 field role for Xerox, I drive to sites across the region and fix whatever's wrong with the printer, and "the printer" can mean gears and wiring, the circuitry, the firmware, or the network. Some of those repairs go deep.
The one that stands out is replacing the developer delivery system on a VersaLink C415. Getting to it means taking the machine most of the way apart: removing the parts and wiring in front of it, making the change, and putting it all back exactly as it was. I've done that teardown about six times on the C415, and similar full teardowns on the B400, the B8000, B8100 and B8200, the C8100 and C8200, and the Phaser 3655 series.
What I did
My method is the same one I use everywhere: I photograph each step as I go, so every wire goes back in the right place, and I keep the service manual open as the reference for parts and how they fit together.
The result
The first time was genuinely intimidating, and finishing it was a huge feeling of accomplishment; the printer worked perfectly afterward. Now, each time a repair this deep comes up, I set a goal to do it faster while keeping the same accuracy.