These are two good articles on the restoration or repair of a Swan Visofil.
The US version of the original patent for the Visofil mechanism can be found by clicking on the image below
The important thing to know about a Visofil is that the rubber sac has to be cut to form a tube. This tube is shellacked to the nipple on the end of the section, as well as the nipple on the end of the ink reservoir. The spring (as can be seen in the drawing above) coils around the rubber, pushing the reservoir away from the section.