I think 3D printed parts using 'white strong flexible' from Shapeways or a material of similar properties would be OK, certainly once you had the CAD model, you could print a couple and if in a few years the part failed you could replace it.

The trick with replicating any part is getting sizes and tolerances accurate enough to work with the existing design. material shrinkage (while cooling/setting), interference fit (for pins), gear ratio, tooth angle, screw thread etc etc would all need to be accurately replicated.

I've thought about doing something similar with classic parts made from gold plastic, if the part is simple enough and doesn't have any deep crevices shapeways have a treatment that smooths the surface so it appears less grainy.

I don't think home 3D printers would produce a material quality that would be very reliable in smaller parts and it looks awful if being considered for parts that are visible.