I got fed up of the PTFE guide tubes slumping forward and down so set out to find a guide for them. All of the ones I found dodn't really do it for me so I fired up Fusion to make my own. The arm swings up and down to allow for free movement of the tubes.

I did see the dovetail method of holding on to the top bar but I can't remember where. If it was your model please let me know so I can acknowledge you.

Requires one M3x20 machine screw for the pivot point. Slightly shorter should work fine instead. It threads into a 2.5mm hole. I ran an M3 tap through first.