Whilst printing a 16th set of Mendel parts, my Mendel printed a bed of brackets with bits missing: -
On investigation I found the idler bracket on the extruder had broken, so there wasn't any pressure on the pinch wheel.
It lasted a long time before it broke but clearly it wasn't strong enough. Wade made his in PLA, which is harder and I only use two of the four bolt holes, so mine is under more strain.
I made a stronger replacement. It is thicker and a little bit bigger in the other two dimensions. I also made the holes 4.5mm rather than 4mm so it slides on the bolts easier and I capped the ends of the axle holder as mine tended to slide sideways.
The files are on Thingiverse.