Checking Sash Guides
WARNING: This page is about a different car, the 2020 Porsche Cayenne and 2019 Porsche Cayenne. However, it is still accessible from the selected car via links, so may be relevant.
Plastic-coated covers show fine, parallel scores after the belt system has been subjected to stress (seat belt buckled during accident). On the other hand, wear caused by frequent use is indicated by a stripe-free, smooth surface.
Inspect the sash guides for distortion, flaking and crack formation.
In the event of scoring and/or damage, the entire seat belt and seat-belt buckle must be replaced.