This was off the 1976 four-door Cadillac Seville and is the driver side headrest.  These have an offset to them so the driver side will not work on the passenger side.

The armrest isn't pretty good shape with no rips or tears however there is a slight change up white dusting marks I'm not sure what the origin is almost looks like aerosol pain overspray.  It's not real prominent but I pointed out in the last picture.