Under the Hood it is the little nipples on the main Vacuum Line to the Power Brake Booster that crack off, the short sections of rubber vacuum hose that coonect the plastic vac tubes and the 3 or 4 way rubber connectors.

Inside of the car there is the same rubber stuff but on mine I found that all the rubber stuff looked new.

Where the Plastic tubing has issues is in the area where the door hinges; other wise nothing much happens to the plastic tubing.

You can use regular Vaccum Hose cut into sections to replace the tube to tube connectors and the 3 and 4 way conneectors are not too expensive if you shop around.

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84 300D, 82 Volvo 244Gl Diesel