I would start with a new set of PBR Deluxe front pads and if that doesn't work then change the rotors too.

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2G91CGNF72GM01YM43&yearid=1988@@1988&makeid=MB@@MB@@X&modelid=300%2DE%2D002@@300E&catid=N@@Brake&subcatid=N1010@@Brake+Pad+Set&mode=PA&subcatid=N1010@@Brake%20Pad%20Set&applicationid=000038707&source=www.peachparts.com&clientid=catalog.mercedesshop