rotations of the manipulation unit 4 around the axis of rotation r an o ring seal 13 in the edge 10 ensures that the wear ring 12 is sealed off relative to the raised edge 10 the o ring seal 13 is sunk into the raised edge 10 approximately centrally in relation to the wear ring 12 a radial shaft seal 14 is provided opposite the o ring seal 13 the wear ring 12 is held in a way that provides a seal between the o ring seal 13 and the radial shaft seal 14 like the o ring seal 13 the radial shaft seal 14 is rotationally symmetrical about the axis of rotation r the radial shaft seal 14 is held in a receiving space that radially widens the annular groove 11 a capillary barrier 15 is provided at the edge of the manipulation unit 4 in conjunction with the o ring seal 13 and the radial shaft seal 14 the capillary barrier 15 ensures that no fluid such as cleaning fluid enters the interior of the drive housing 7 via the intermediate space between the lid 7 u2032 and the underside of the manipulation unit 4 in addition the drive housing 7 has one or more centering rings 16 encircling its circumference these circumferential centering rings 16 ensure that the lid 7 u2032 is received and held centrally in relation to the axis of rotation r at the top of the otherwise pot shaped drive housing 7 an additional further seal 17 in the region.