MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
i changed the variable "mountPlate" and uploaded the file (MyExtruder_NoMount.stl) for you.
Just split the file in your Slicer, if you want to print the idler separat.
Also, you can easily modify the extruder with openScad to your needs - try it, it's pretty simple :)
The used mount-thingi with the red one is a modified version from http://www.thingiverse.com/thing:1357814.
.. hope, you'll like it :)