Hi, my best friends Replicator 2 recently broke. Does anyone know if he would be able to buy extruders which are not specifically made for the Replicator (or other Makerbot) printers and use them on his printer to replace the broken extruder that he has, or does it have to be a part made specifically for the Replicator 2? If so, where would he find one? Does Makerbot sell them?