Background
The channel that separates the roof metal skin from the side panels is filled in with a long metal rail cushioned with a rubber footing. Since this piece runs beyond the roof cut line, the rail must be modified, and the roof channel re-formed.
Drip molding
Roof channels, common on many modern cars, evolved for several reasons. The channel design initially facilitated the use of smaller welded panels without the added expense of adding lead filler for a smooth roof line.
In real world use, it became evident that the channels also minimized roof “drumming” caused by panel vibration from wind and road conditions. To cover the channels, drip rails were developed to help keep water off the sides of the vehicle.
All New Beetles use 1C0 853 701 (left) and 1C0 853 702 (right) drip rails. Note that this part may be referred to as a rain gutter, roof trim, or roof molding (British spelling is moulding).
Good tip! Thanks!