Redesigned extruder block with smaller drive gear hole (11.8 instead of 13 mm) -> longer filament support between the drive gear and hot end so flexible filament does not get stuck in between.
As CTC that I own is an Makerbot Replicator 1 (dual) clone, it should also work for Makerbot Replicator 1 and FlashForge printers.
Update 01.04.2015: Changed hole diameter to 11.8 so it does not need sanding, moved filament hole a bit, made a bigger diameter hole on the bottom so it does not touch the gear fastening screw
Update 31.03.2016: as no changes have been made for a long time I'm unchecking the WIP marker of this thing
Update 26.06.2015: now 2 files are available: for left and right extruder
CTC - Makerbot 1 (Dual) clone
Best printed in ABS or Nylon as even the cold end of the extrude can get quite hot on some printers and with some materials.