A friend's S320 SWB (.032) has a coolant leak. I found the issue and its a T connector on the second firewall and its located right behind the oil filter housing( M104).

I can't find the part in the EPC, other parts websites and this one lack an exploded view of the engine compartment and systems so its hard.

But here and everywhere else the connector is shown with 4 connections. Whereas the one I have only has 3, I am sure it only has 3.

flickr is being lame so I can only give a link to the pic

http://www.flickr.com/photos/jrgfoto/5348953851/