Lastly, here is me moving the gantry pushing on the left side (side with the worst bearing imo):
Towards the end of the video you can hear it bind several times as it runs along.
Sadly, I've also pushed the gantry around without that bad bearing attached and I still get these binding issues. However, perhaps that could be a symptom of simply not having equal load support without that 4th bearing attached? Who knows...
Chris