If I understand this right, the vertical portion of the pipe is fixed to the floor and the horizontal part is in the slide. To me, this means you have a long slot in the bottom of your slide for the floor end to pass thru as the slide goes in and out. Interesting. Seems like this would put a lot of twist stress on the pex joint,,, hence the problem you found.
I have a 2010 version of a 2900D and it's very different: no slot, no pex. What keeps freezing cold air from coming in that slot when the slide is out? Or critters?
In my 2900, I can see a long flex hose (with screw clamps on the ends) between the bed and the baseboard. It just follows wherever the bed and slide goes.
Larry