A motor vehicle side door includes a glass panel, a frame, and an elastomer run seal. The elastomer run seal includes at least one protruding rib that is located and dimensioned so as to be able to come into abutment against a free end of an inner wall of the frame when the at least one ascending strand is in a preliminary mounting position on the frame, and to be able to come into abutment against an inner wall of the frame when the at least one ascending strand is in a final mounting position on the frame, a gap between both inner and outer walls having a size which is higher when the run seal is in the preliminary mounting position than when it is in the final mounting position.