A motor vehicle side door, comprising: a) a glass panel having an outer face and an inner face and carrying a panel guide secured onto said inner face, said glass panel being able to be moved from an upright position to a downright position, b) a frame that is configured to extend along edges of the glass panel when the glass panel is in said upright position, the frame including a vertical edge element which is adjacent to the glass panel when it is in said upright position and which has an outer surface laterally flush with said outer face, said vertical edge element comprising a U-shaped portion in cross section including an outer wall which is parallel to said glass panel and which includes said outer surface, an inner wall which is parallel to said glass panel, and a connecting wall connecting said outer wall to said inner wall, c) an elastomer run seal mounted on the frame and suitable for receiving said glass panel when moving, the run seal comprising at least one ascending strand configured to be mounted at least in part in said U-shaped portion, said at least one ascending strand having an outer branch configured to be in contact with said outer wall and to be sealably in contact with said glass panel, an inner branch able to be in contact with said inner wall, and a connecting branch connecting said outer branch to said inner branch, an outer face of said inner branch and an inner face of said outer branch defining therebetween a gap which extends in a first plane substantially perpendicular to said glass panel and which is configured to be crossed by said panel guide, said outer branch comprising a groove that is able to receive at least one hook of said panel guide, said inner branch comprising an inner face comprising at least one protruding rib (58, 60) which is able to be in contact with an outer face of said inner wall or against an outer face of the frame, characterized in that said at least one protruding rib (58, 60) is located and dimensioned so as to be able to come into abutment against a free end (30b, 18d) of said inner wall or of said frame when said at least one ascending strand is in a preliminary mounting position on the frame, and to be able to come into abutment against said outer face of said inner wall or against said outer face of said frame when said at least one ascending strand is in a final mounting position on the frame, moving of said at least one ascending strand from the preliminary mounting position to the final mounting position being realized in a direction (H1, H2) substantially perpendicular to said first plane, and said gap having a size (W, W) measured in said first plane which is higher when the run seal is in the preliminary mounting position than when it is in the final mounting position. a) a glass panel having an outer face and an inner face and carrying a panel guide secured onto said inner face, said glass panel being able to be moved from an upright position to a downright position, b) a frame that is configured to extend along edges of the glass panel when the glass panel is in said upright position, the frame including a vertical edge element which is adjacent to the glass panel when it is in said upright position and which has an outer surface laterally flush with said outer face, said vertical edge element comprising a U-shaped portion in cross section including an outer wall which is parallel to said glass panel and which includes said outer surface, an inner wall which is parallel to said glass panel, and a connecting wall connecting said outer wall to said inner wall, c) an elastomer run seal mounted on the frame and suitable for receiving said glass panel when moving, the run seal comprising at least one ascending strand configured to be mounted at least in part in said U-shaped portion, said at least one ascending strand having an outer branch configured to be in contact with said outer wall and to be sealably in contact with said glass panel, an inner branch able to be in contact with said inner wall, and a connecting branch connecting said outer branch to said inner branch, an outer face of said inner branch and an inner face of said outer branch defining therebetween a gap which extends in a first plane substantially perpendicular to said glass panel and which is configured to be crossed by said panel guide, said outer branch comprising a groove that is able to receive at least one hook of said panel guide, said inner branch comprising an inner face comprising at least one protruding rib (58, 60) which is able to be in contact with an outer face of said inner wall or against an outer face of the frame,