The roller guide on the top sliding door is the only one visible. To protect it and give it a neat finish, it is covered by a plastic cap or cover.
This cap snaps onto the metal of the roller guide, and as long as you don't touch it, it stays in place. Once disassembled, you may find that the plastic has become abrasive over the years. If it cracks or chips, the only thing you can do is replace the cap.
Useful information from Paruzzi magazine and from our YouTube channel :
Look for more technical articles on the page Paruzzi Magazine