On the underside of the headlight housing is a drainage tube that drains off any incoming water or condensation to prevent moisture and therefore corrosion.
If these drainage tubes are missing, water splashes can enter them, which can become a breeding ground for rust.
Volkswagen revised this tube for the Volkswagen Beetle in 1966, after which the same tube was used as for the Karmann Ghia, these were equipped with an additional attachment so that moisture could go outside but not inside. The tube used until 1966 didn't have this extra fixation, theoretically it can still have water splashes inside although the chance of this happening is very small.
If you own a Volkswagen Type 3, the tulle used for the Beetle's headlight pots until 1966 is also used in the rear fenders.
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