The lower dash in your W126 is very similar to my W116, so they probably attached the same way. After I remove the screws it just pulls off. There are a couple of plastic tabs attached to the carpeted piece. They go into metal clips in the dash itself. Like I said though the carpeted panel should just pop out if you have removed all of the screws. Like everything you do for the first time, take it slow. I am sure alot of us have yanked on some plastic part just a little to hard and snap.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member