Engine vent smoking on mercedes 190d

[boooney]

Hi-

I have a 1984 190d 2.2 with 4 cylinder engine (non-turbo) that has a small hole in the cylinder head cover on the passenger side. According to the manual, this is to vent the diaphragm chamber in the pressure control valve (see pic below) It smokes a lot through that hole and when I'm idling, the smell gets blown into the car through the climate control air vents. Pretty smelly and nasty.

Does anyone know if I can
1. block this hole (on another 190d I looked at, the hole appeared to be hidden/blocked with a sticker); or
2. reduce the smell through the climate control vents by another means? I don't know where the climate control vent draws the air from, so perhaps I could make sure it's not drawing in the smoke.

Any ideas would be most appreciated. Thanks.