Welcome to the community.
By “rubber thing” are you referring to the through-Hole grommet?
I’ve moved on from this design and printed a PETG passthrough which is hard screwed into the frame. I then use two PTFE tubes for strain relief. I got sick and tired of Bambu’s crappy design which pops out too easily if you are let’s say feeding from a dryer box.
This is the solution I use today.
https://www.printables.com/model/348617-bambu-lab-p1p-ptfe-tube-bracket-remix
This is a wonderful design that Bambu should have started out with. Note, these are divided into two pieces by the designer so that they print flush. In my case, I used acrylic cement to weld the two parts together as one unit. I made the hole undersized using the X-Y hole compensation in the slicer and then enlarged it. I then I used a drill to enlarge the hole slightly so that the PTFE tube would pass through more easily. Used PTEG filament to ensure that it would not warp due to chamber heat and for strength.
Here it is in action. You’ll note that I placed a PTFE tube through the interface hole and secured it with PTFE hydraulic fittings on both sides to prevent the tube from slipping out. The PTFE tubes provide sufficient strain relief, frictionless flow, and the rigid plastic allowed me to secure the whole setup using screws, unlike the floppy mess caused by the rubber grommet.
Note: You may need to drill screw holes through the steel case. My unit had partial holes, possibly due to the P1S back panel retrofit. An X1C or P1S may have these already pre-drilled. I used an M3 tap for threads and screws, but you could likely self-tap the screws. I tapped threads for easier servicing.
Interior view
Exterior view
Tools an accessories used.
Here are the items I keep on hand as part of my everyday 3D printing toolkit that were used to create this solution.
Tap kit. I used this for cutting threads in PC and PETG in lieu of heated brass inserts. For M3 and larger screws, it’s actually stronger than brass when placing threads close to the thin outer wall of the model.
These are Philips head screws that are seen in the photos. I find Philips head more convenient because I simply have more Philips head screw drivers lying around my lab and shop.
https://www.amazon.com/dp/B07C6J6FXF/
But if you want to give it a more authentic Bambu “Factory Look”. These are the hex button screws that are used in various parts of the printer.
Here are alternates that include M2.5. I couldn’t find a button head set but these will do in a pinch if you lose a Bambu factory supplied screw.