Any idea how to remove the slider knob that controls the center vents?[/quote]

IF you mean the slider knob that allows you to move from forced air only to passive fresh air, then you have to remove the speaker grill and speaker from the center dash. The slider knob is attached to a flip-style air manifold (right word??) via a rod that screws into a connection and has a locking nut on it and you get to it from the top through the speaker hole in the dash. At least that is how it is on my 75 240D. Good luck, Alex

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"Frau Blue Car" 1980 240D think Frau Bluker, cue the horses, formerly known as "China" from JimmyL
"Gunther" 1982 300D.....Turbo!! A/C!! Sunroof!!
"Fraulein" 1975 240D----Donated to NPR