The default idler splits between layers after repeated tightening, it also can't be made sufficiently tight on hobbed bolts cut any deeper than their own bolt which is " widely considered the best hobbed bolt on the market", they really said that. Anyway, I made a clone in openscad that prints the other way up so the layer bonding is no longer an issue. It should be printed in PLA, ABS will flex and weaken over time, PLA is more rigid. As you can see in the video it slots in as nicely as the original. Any issues, let me know and I'll see about improving the part. http://youtu.be/HmJ9fMMfU7oPrint in PLA. STLs with and without support provided.