I noticed the cable chain from the extruder to the z-axis arm slopes down toward the z-axis end, this was causing one of the links to pull apart slightly.

Update you are better off using the remix of this as it improves the design :-)
http://www.thingiverse.com/thing:1421438

So I created this small riser plate, which is nice and simple and does the job perfectly. It's 22mm x 20mm x 4mm the 4 holes are 3mm, I didn't have the correct length screws so used nuts as spacers where necessary (as the photos show).

This was printed at 200 microns and 50% infill, taking less than 15 minutes to print and fit.