Abstract: The hydraulic chamber (2) of a hydraulic swivel motor comprises a lateral opening which is closed by means of a cover (8). The seal of the hydraulic chamber with respect to the surroundings is achieved by a circumferential cover seal (12) which is produced by friction stir welding. The weld root (12?) extends to the vicinity of the faces of a sealing strip (10) which is provided between a shaft (4) and the cover (8) for separating two working chambers (A, B). This measure prevents leakage to the surroundings, on the one hand, and minimizes leakage between the working chambers (A, B), on the other hand.