This is a little late but I figured I'd share just in case someone is in need.

To make an exact copy of a small obsolete plastic part you simply take a master part and cover it with a release agent and then cast material around it.  Once the material is cured you cut it open and remove the master part and are left with a perfect cavity.  You then fill the empty cavity with whatever material you want your part to be and let it cure.

(I'm leaving out many of the little details since this has been discussed before.  Also, this is for a single piece mold, many parts would require a two piece "clam shell" type mold.)

Picture #1:  The parts to the left are the originals/masters  (top is handmade using existing parts, the bottom is a SLA).  The parts on the right are cast copies.
http://files.photojerk.com/t3/rapidmolding_1.JPG

Picture #2:  The cast mold will pick up the finest details which in return show up in the parts cast in the mold.  It's a poor photo.
http://files.photojerk.com/t3/rapidmolding_2.JPG

This method is a great way to cheaply (relatively speaking) make duplicates of parts once you've done it a few times.  Look out for air bubbles.

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