This version adds a small ridge under the extruder gear cutout to fill in the gap where the NinjaFlex was getting jammed between the gear and the support piece. If you use this part, the extruder gear needs to be aligned with the raised ridge of the support part.
Like the original part, you'll need two short M3 flathead machine screws. I couldn't find any that short locally so I cut down longer screws.
Update 8/5/2014: Added a new version that has small changes that make it easier to use. I haven't gone back and tried NinjaFlex again though (the original version worked for 3-5 hour NinjaFlex prints without any issue, hopefully the new version will do the same). Also added the stl file for the bearing washer I use to offset the bearing a bit (the file has two washers but you should only need one).