You need this:
http://catalog.peachparts.com/ShopByVehicle.epc?q=1995-Mercedes--Benz-E320--Sedan-Cooling--System&yearid=1995%40%401995&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6392%3ABT|5%3AED|10000022%3AMBC|1508%40%40E320+Sedan&catid=240909%40%40Cooling+System&subcatid=240927@@Radiator+Fitting&mode=PD

It's the fitting to the hose from the radiator to the expansion tank. The short part of it is broken and fell into the radiator; it does not look like you have enough to hold it in place when the car gets hot. Easy, cheap, 1-minute fix.

Don't delay-- you can lose a lot of coolant through that outlet.

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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black