Several older cars used this system for their window closure. A plastic part slides through a rail and therefore wears out. A metal handle is riveted to the plastic part. When the plastic is worn out, the entire mechanism must be replaced. That is now over. 3D Classics developed a new part in consultation with some owners of a Karmann and a Volkswagen. This is more robust and replaceable. 2 parts fit together well. Glue or melt them together around the metal handle.