Well, it took me a while to take a picture but here it is. Yes, It is a w124. I cannot find a spot where this hose connects to for the life of me... If I squeeze the radiator hose, I can feel the air freely coming out of this small hose.
Also is this used to block this hose? Or is this for something else?
http://www.**********.com/search/product.aspx?sid=umejld45xkrz0ayx2elsacae&makeid=800016@Mercedes&modelid=1195534@E300D&year=1995&cid=16@Cooling System&gid=2066@Expansion Tank Plug