Re: materials ?!
Obviously there are reasons why certain materials were chosen to make the original parts, but if you are in space and an important part breaks or goes missing you are going to have to find a substitute, which will be neither the right shape nor the right material. A 3D printer would at least solve the first problem; the second, you use materials that can be put to a variety of potential uses. You might be able to keep a variety of 3D printing compounds around - say, one for resistance to heat, another to cold, another for flexibility. Keep a few 3D printers on board instead of a storeroom full of spare parts most of which will never get used. Develop parts that allow you to improve or extend the apparatus for scientific experiments that were conceived many years ago. This is the closest you get to having a factory on board. It sounds almost inevitable assuming the technology actually works in space.