For surface details (seals, emblems etc.) or flatter shapes you can make a simple press-mould.
You push the original into a flattened ball of putty (possibly lubricated with talc, Vaseline, vegetable oil) and wait for it to nearly set, then remove the master. When the mould has cured you can press fresh putty into it and peel out really very good copies of the original part; best to wait for it to be set or nearly set before trimming down to size, to prevent distortion.
Einion