The sunroof guides have little felt-covered rubber feet that wear out and disintegrate. Replacing them is involved enough you should have a good diagram to guide you. Parts available from FastLane and others.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1KX04M32Z1LV1BKPE5&year=1989&make=MB&model=300-E-002&category=O&part=Sunroof+Guide+Jaw

They call them 'guide jaws', and there are quite a few in the assembly.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7