Found the site that describes the vacumm pipes on the 280 110 engines.
To Quote.... The plastic pipe from the nipple on the valve cover vent hose is to supply a low vacumm draw to the "Fuel Pressure Damper" in order to prevent the possibility any vapour from escaping to the atmosphere. Purely a precaution by Mercedes as it probably does not exist on any other K Jetronic System fitted by other vehicle manufacturers ? ? It does not effect any engine function.
Now I can go away and die...