Run the swivel up and down without the sail.
If it binds , releases and binds again look for
damage to the foil esp. at the section joins.
If the forestay is slack the screws fret in the holes
causing a minor misalignment between sections.
Also look for dimples and flaring at the joins.
If it binds all the way down its possible the internal
plastic (nylon?) sleeve has expanded due to time and
exposure to hydro carbons used to lubricate the track.
If it goes up and down easily without the sail then the likely culprit is damage or wear on the bolt
rope.