Sorry for not responding for a while, was on a business trip. The M3 type inserts I was using were cheap chinese ones with a straight knurl on both sides. I have since purchased some tapered ones with a little more sophisticated geometry, these appear to seat a little more firmly in the XY carriers.
The tight wire routing is actually for installation of the molex fitting (or removal).
I added a chamfer, see above image. It might be too much as it appears to be close to interfering with press-fit holes. Ideally the chamber should only go on the outside edge to facilitate the molex sliding in at an angle.
On a side note, the XY carriage assembly needs M3 pressfit deep into the housing correct? How deep did you go?
Lastly, instead of reprinting the carriage I was going to try heat setting the bushings instead of ABS. Have you ever tried this? Heating up the bushing like you would a press-fit insert? I would hope this would reduce the stress on the layers as ABS is pretty damaging.