The only problem I can see is that there doesn't appear to be a cabin vent...

All modern cars have flaps that allow positive pressure from inside the cabin to escape, even my Mk1 Golf had seals in the door panel; W123s may have this too, but if they do I am unaware of where they are. Without them, I could see a possibility of a problem.

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1998 VW Cabrio
2001 Audi SomeRoad A/T (no air suspension)
2003 Audi DeadRoad M/T (no vroom, for later)
2002 Audi NoRoad A/T (nothing under the hood, being rebuilt)