I can't help you with the armrest, but there is a hidden release under the material on the back of the seat for the headrests, at least on my seats. Feel around and you will find it. Press it down, pull, and the headrests will come off.

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86 560SL
With homebrew first gear start!
85 380SL
Daily Driver Project

http://juliepalooza.8m.com/sl/mercedes.htm