The seal comprises a casing made of two portions (1, 2) crimped into one another with an accurate hermetic position adjustment at interfaces (15, 6b) and a composite structure comprising inside the casing an advantageously flexible and resilient core (24) and a winding (20) of brush bristles. This structure directly extends facing internal faces (9, 10) facing each other in the casing, which compresses the same and has an arcuate shape having a slightly higher radius of curvature. The composite structure is held at an accurate position, firmly but free of constraint.