Most likely vac line disconnect is the one that goes under the front cover in front of the engine..you have to remove the plastic cover. That line goes to the EGR Switch-Over valve and is a plastic line....they crack from heat fatique and should be rep[aced with a rubber line.
The plug connectors you want to change are the ones under the 3 coils, not the 1st and 3rd in the pic shown. The 2nd one .

This one is the common misfire culprit on all 104 engines.

http://catalog.worldpac.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=21H0MN3YU26C16TZ6M&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1995&product=F1010-84561&application=000357354

If you change plugs , use ONLY Bosch F8DC4/standard copper core..
NO PLATS !!!!

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=21H0MN3YU26C170AWJ&year=1995&make=MB&model=C-280-001&category=F&part=Spark+Plug