I have a beautiful 1984 380SE with a nasty problem:

When I open a window (just one), the slight underpressure in the cabin pulls in gasoline vapours from the engine room.
(When more windows are open the problem goes away as the pressure is levele. Also it should be noted that the problem is not there when all windows are closed. Again I assume it is because there is no underpressure in the cabin then)

I heard a rumour that this may be due to the gas-pipe running from the gas tank to the engine, being pulled apart at a joint behind the glove compartment by the underpressure.
I have now tried two Mercedes mechanics with no luck.

Have anybody experienced or heard about this problem?
Or have other suggestions?

best wishes
/Lundbye