A device for a window lifter of a vehicle door includes a cable winding drum disposed inside a housing of a casing and a seal attached to the casing. The seal includes a stop portion that prevents translational movement of the drum along its rotational axis while still allowing the drum to rotate freely about the axis. The inventive device allows the drum to be held in the housing before the casing is mounted on a dividing panel without requiring auxiliary parts to hold the drum in place and without compromising the seal when the casing is fastened to or removed from the dividing panel.