MB servicing info available at the following:

http://mb.braingears.com/

On a lot of models, it's just to the left of battery(as seen from passenger position) and back along firewall.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1EQ0PTV2S1QT0XA677&year=1988&make=MB&model=190-E-004&category=R&part=Heater+Valve

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"