usually under the hood they have a diagram left of the radiator. unless it has come off .. u have two of those valves and they go on a certain way .. notice how one is bent/angled .. if you have a junk yard holding some mercedes i suggest u go check it out...

u can snag one from the yard if they dont break when you pull the vaccum line off .. just twist it clockwise and counter clockwise before pulling up on the line http://www.***************/search/product.aspx?sid=bpubspzwghn****od1bpri55&makeid=800016@Mercedes&modelid=1194094@300SE&year=1988&cid=18@Electrical%20%26%20Vacuum&gid=4604@Thermo%20Vacuum%20Switch


check this site out