sounds like they wanted to heat the head evenly and to prevent air pockets. Its a pretty high point in the system, It would become nightmarish trying to purge the trapped air if it did not have such a setup.

Good point. I think that's why the instructions for filling the cooling system always say to park the car nose uphill if at all possible and run the car with the heater in Defrost (forces full heat).

Jeremy

Nick Stauer of MBSR made it right!
 

To follow up to the earlier posts, Mercedes has reimbursed me for the $500 I spent (back in January 2013!) on the first (of three) replacement monovalves (all of which cracked and leaked). This reimbursement happened when the local service manager, Nick Stauer, of Mercedes-Benz Santa Rosa (California), spoke to the new factory rep for our area. She agreed to put in a request for a "reimbursement for leaking monovalve" (their words) and it was honored. I got the check yesterday.

This was on top of replacing the monovalve once themselves at no cost to me. Their replacement lasted less than a month but it confirmed I wasn't doing anything wrong when I did the work. So their actions are definitely above and beyond what one expects from car dealerships. I am pleased. All hail Nick Stauer and Mercedez-Benz of Santa Rosa (aka Smothers European).

That it took three years is unfortunate (better for them if I had sold the car or died or moved away). Once I had patched the original monovalve (stopping the leak) the pressure was off and I didn't push as hard as I might have done.

It also suggests that the factory has no intention of getting their subcontractor to build a new, non-cracking part. This I expected from the beginning; why go to a lot of work to re-design a one-off component used in 3,000 cars 20 years ago? BTW, a new monovalve/pump (001-830-40-84) is now $900 or so I've been told. Caveat emptor!