3-D printing gives unprecedented capability to rapid prototype and test new designs. Here is an example of a part that, because of its age, can not be obtained thru any source. The aircraft is a custom R/C Helicopter that incurred some damage to its main drive gear. This part is no longer available, so I took the old part, and generated a 3-d model in CAD.
From this point I contacted another manufacturer who was able to produce the part out of glass reinforced Nylon using a laser sintering process. The end result is very strong, and perfectly duplicated the original part.