As far as I know the 140s with the electric headrest can't drop back for improved visibility. At least the earlier models couldn't. I'm not too sure if they changed it later on. I've seen a 93 600SEL and the headrests were part of the rear seat and they only moved up a down like the ones in the front.
[Edited by vinamg on 04-16-2001 at 07:46 AM]