replicator 2x Edit
http://www.ebay.com/itm/121180622234?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT This is a POLY URETHANE, MANUAL CAST kit to prevent melting/warping problem in long extrusions. It is an upgrade kit for the Delrin Plunger. It replaces the existing plunger in Makerbot Replicator 2X. It is not compatible with Replicator 1 Dual. If you are experiencing print failures every time you use a new filament, that is because of the existing plunger on your extruder that cannot adapt to the diameter tolerance of the cheaper filaments. I have had issues even with some of the Makerbot filaments, but this upgrade will solve this issue. You are buying a Makerbot Delrin Plunger replacement kit/Extruder Upgrade kit as shown in the first image. This is a picture of the actual item you will get(stepper motor/drive gear not included). This kit includes everything needed to replace the delrin plungers on your Makerbot Replicator 2X with a spring-loaded ball bearing assembly.
http://www.ebay.com/itm/Makerbot-Replicator-2-Delrin-Plunger-Extruder-Upgrade-Kit-Printed-version-/121103618952?pt=LH_DefaultDomain_0&hash=item1c32569388 Makerbot Delrin plunger , see http://www.3dprintingstore.co.za/extruders-hotends/minimalist-extruder-kit-for-1-75-3mm-filament/
http://www.reddit.com/r/3Dprinting/comments/26bt91/makerbot_steals_yet_another_design_we_need_to/ if anyone has not already seen this. Makerbot seems to have also patented an auto bed leveling design from Steve Graber, the guy who designed the Cerberus line of Delta 3D Printers.
Quick release extruder Edit
http://www.patentbuddy.com/Patent/7384255 two wheels against each other