I can see that a red adhesive had been used to adhere the bearing to its Y-axis parent, but not successfully. I will ask Nathan, the head engineer at QU-BD what adhesive I should use to make sure it stays put the next time.
The second problem that I encountered is more important, notably the Z-axis end-stop. The X and Y end-stops are not that important because they do not dictate one of the most critical factors in 3D printing: how close is the first layer to the bed. I have found that the mechanical end-stop on the Z axis of the RXL to be finicky. On a couple of occasions, I tried to home my axes and the Z end-stop did not trigger. This was bad. I quickly hit the Emergency Stop and then spent some time re-aligning the bed. Right now, there is no good way to calibrate the Z axis. There is a screw-hole at every corner of the bed but only two screws were installed. This leaves the mechanical Z-limit switch -- something that I have found works differently from one moment to the next. Home it when the bed is cold, it is a certain distance from the bed. Try it when the bed is hot, something different. Right now, the only way to tweak your Z limit is to carefully bend the Z limit switch lever. My suggestion to QU-BD is that they leave mechanical end-stops on the X and Y axes but that they substitute their Z mechanical endstop with something more precise like a hall-effect end-stop or opto-end stop and that they provide a screw to adjust it.
I don't want to seem overly-critical. This is nothing short of a groundbreaking machine. When I look at it, I see a labor of love; something I would be proud to release to the world.