Drop in Paxtruder for MakerBot

This design is a derivative of the Paxtruder-0.2:
http://www.thingiverse.com/thing:1125

My idler wheel cracked about 2 weeks ago so I though it would be a good time to experiment with the Paxtruder design a bit. I planned on making it a weekend project because I had plenty of acrylic around and I had some 1/2\" thick acetal scrap to make a pusher but, unfortunately, I had to put in an order to McMaster to finish this guy so it didn\'t get completed till now.

I wanted a drop in replaceme