Summary

UPDATE October 28, 2013: I've uploaded an improved version (Upper Filament Guide 2) that makes the hole a little smaller, and moves it a little closer to the stepper motor. This results in much improved reliability.

I noticed recently that my MendelMax 2.0 was squeaking whenever the filament was being retracted or re-engaged during printing. When I looked closer, I noticed that the upper filament guide that came with my printer was flexing up and down at the same time. The delamination was obvious (black part in photo) once I removed it from the printer. Not good.

After printing a replacement part and discovering it also squeaked, I designed a new part. This has a thinner hole that is larger, so there is less friction between the filament and the guide. The new one works perfectly.