The vacuum tube from the brake booster to the motor is connected by means of rubber bushings for a tight connection.
In the worst case, a leak at the brake servo can even damage the motor, so it is important that the vacuum loss is resolved as quickly as possible. A common problem is leaking connections when the mounting rubbers (sleeves) have dried and no longer close properly. If you squeeze the rubber and cracks appear, this is a sign of dehydration and replacement is necessary.
In later years of the Volkswagen Vanagon, this rubber was also used to connect the fuel tank venting hose to the filler neck.
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