The heater hose coming out of the firewall into the head is returning coolant from the heater core back to the motor.

You refer to the "U shaped hose" if you mean you are looking at the Mercedes parts diagram, they show a U shaped hose but their parts diagrams are representative, not necessarily accurate. They in fact list six part numbers for that hose, dependent on model, and they are all different. (I happen to be shopping for one, so I know this.)

Many cars no longer have the factory hose and just have a generic length of hose installed there, or have the incorrect part number installed -- as is the case with my 300td -- and it's a royal pain to work around it.

You don't need a hose clamp to replace the element in the monovalve. You will get some minor spillage but that is normal.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22