I have an inexpensive rotary tool that I have dedicated to use with a rotary flex shaft attachment. A few days ago the rocker power switch stopped working and I could tell something mechanical broke inside. These switches are generally simple devices, so I decided to pull the top switch piece out to see what failed. Note, be sure to mark the switch so you know the correct way to put it back together. I put a silver sharpie mark on the open/off side.
You can see in the picture that the tube holding and guiding the spring part cracked and broke.
Decided to 3D print a tiny insert to reinforce the spring tube. (PLA with 100% infill)
The first time I put it back together I got a good switch click feel but the contact was not closing. Figured it was being blocked by excess insert material. So I popped it back out, sanded the bottom surface to make it sit lower and put an outside taper on the top edge of the tube.
Worked this time.
It was bit tricky to get it back together with all the parts staying in place. Placed the teeter-totter contact in place and tilted the switch body to the side. Carefully inserted the switch top with the spring in place and slowly, but firmly, pressed together.
It’s now fully functional again. 
A perfectly viable alternative would have been to completely remove the original broken tube and 3D print a full insert replacement. Maybe adding a bit of glue to make sure it stays in place.
This was my backup plan if the other way didn’t work. In hindsight I probably should have just done this to begin with as there would be less material to potentially block the contact from closing.
