Low cost parts, regardless of little or no market demand. 3D printing is here now.

I wonder if you can use fuel-proof materials...

The 3D printed parts are pretty delicate. There is a 3D printer where I work but do not have access to it:(

This technology is not new. I was working with 3D printed prototypes 13 years ago. If you dropped one on the floor you had to get a broom to sweep up the pieces. New materials are stronger but still delicate to say the least. One can make a rubber tool mold from the printed parts though. Then different materials can be poured which will result in a stronger part. This is done all the time for short run prototypes where I work. A rubber tool mold can yield multiple parts in a short amount of time with the fast curing urathanes.

Jason