Try here for adjustments:http://articles.mbz.org/transmission/adjust/
Or if it's a vacuum leak more than likely it is this little cap:http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1ZO0QOK8B2030PE9AT&year=1984&make=MB&model=300-SD-002&category=J&part=AT+Modulator+Cap
If the leak is more extensive, then I would replace it. However, try the other things first because there is more to it than slapping a new one in place.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )