Just a thought - maybe something rolled down there and is blocking the mechanism. Take a small diameter piece of tygon tubing and place it in the end of a vacuum cleaner hose, seal it with tape and push the tube down the rail to see if it latches on to anything like an acorn or something. A word of caution, the headliners for E class are very expensive and sometimes cannot be re-used. You have a wagon? Large rear headliner. The little one for my '94 wagon was about $400 and the total repair job was $1200 (ouch). I think I damaged mine openning it in the winter time when it gets 'stuck' a little before it opens. I think I bent a rail or something.

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dtf
1994 E320 Wagon (Died @ 308,669 miles)
1995 E300 Diesel (228,000)
1999 E300 Turbodiesel ( died @ 255,000)
2006 Toyota Tundra SR5 AC 4X4 (115,000 miles) rusted frame - sold to chop shop
2011 Audi A4 Avant (165,000 miles) Seized engine - donated to Salvation Army
BMW 330 xi 6 speed manual (175,034 miles)
2014 E350 4Matic Wagon 128,000 miles
2018 Dodge Ram 21,000 miles