Hmmm. Absolutely ZERO problems with the Magma here. Sorry you had issues.

My problems have always been my own (although you could chalk them up as design flaws):
- On my Greg's Accessible Extruder, my large gear would seize. FIX: Make sure you use and tighten the second bolt next to the large gear. If not, the hobbed bolt will spin the large gear tighter and tighter towards it. Tighten the large gear nut to the SECOND nut, NOT to the bolt. That will almost always cause problems.
- As suggested by Old Man Emu, the NEMA 17 holes on the Greg's Accessible Extruder are a bit tight. At his recommendation, I pulled the STL for it into SketchUp and lengthened the holes a bit.
- The small gear (attached to the D shaft of the stepper) on the Greg's Accessible Extruder has some VERY thin walls around the nut trap, and it's easy to whiten/break. Also, I brought in the STL and added the D slot to what was originally a round hole, then fortified the nut trap walls to make the chances of breaking less challenging.
- After I added the Prusa i3 Magma ducting with the fan mount and shroud (after modifying to allow the nut at the back clearance), I went from a 7 minute ABS preheat to a 3 minute ABS preheat.

$0.02.