ᐅ Grooves in the seal / lift-and-slide door

Good morning,
after finally managing to clean my lift-and-slide door successfully (see an older thread), I have now discovered grooves in the seal. I have attached two photos: one of the door side and one of the counterpart. I can't explain where they are coming from. Especially since they keep increasing; when I first noticed them, there were 9, and now we have 12. Over time, another groove appears.

If the seal is hollow, a vacuum may form during nighttime cooling, which could cause the dents to be pulled inward from the inside.

Just a thought.

Try moving the camera closer (if necessary, press the detail/flower button to focus).