There's a particular kind of smugness available only to people who own a 3D printer, and it arrives the moment a part of the printer breaks. My Ender 3's filament guide, a small plastic arm that keeps the spool feeding cleanly, sheared off at the mounting hole last weekend. The official answer is to order a replacement. The funnier answer is to print one. The printer, you'll note, was still working. It just couldn't be bothered to keep its own filament tidy.
So I did the obvious thing and went looking on Printables for a guide that someone had already modelled. There were dozens. I picked one with sensible reviews, dropped it into the slicer, and printed it in PETG rather than PLA, because the thing that broke was under constant low-grade stress and PLA creeps over time. That's the whole lesson really: match the material to the job. PLA is lovely and easy and wrong for anything that has to hold tension in a warm room.
The detour was the part hole. The model's mounting hole was modelled for a slightly different bracket revision, and my first print didn't fit. Rather than reprint blind, I opened it in the slicer's measure tool, found I was about 1.5mm out, and grudgingly learned just enough Fusion to edit the hole spacing. Twenty minutes of swearing at sketch constraints, one re-export, and a second print later, it clicked into place with the satisfying snap of something that was meant to be there.
The new guide has now been in service for a few days and it's quieter than the original. Whether that's the PETG or just survivor bias I couldn't say. Either way, the printer fixed itself, which is the closest thing to a self-healing system I own. The broken original is in the bin of shame next to a small graveyard of failed Benchies, where it belongs.