Geeetech plastic extruder arm will crack after sometime. This is a replacement part in case you do not want to upgrade or buy a new kit.
Update: Apr 13, 2020
adjusted hole of filament path by 0.5mm to align with pulley.

After having arms slowly deflect up on me I began to look for a more permanent solution. There are several different types of aluminum and ABS models out there. I took my MK8 design, added the pin and tab found on Whpthomas's version, and made a few modifications to get it printable at Shapeways in stainless steel. I know there were possible tolerance issues considering Shapeways gives a very large tolerance. The part I received measured very close (within .15mm), If you have this made, bear in mind the possible tolerance issue.