Abstract

A mechanism casing for a hydraulic motor comprises a casing body having a face for application of a lid. The lid is applied tightly on the casing body face and fastened to the casing body by screws via screwheads thereof tightened against an outer face of the lid. The screws pass through the lid via screw passages with circumferential clearance between the screws and screw passages. An O-ring is interposed between the casing body and the lid. At least one of the screw passages are conduit screw passages which open out within a perimeter defined by the O-ring. The conduit screw passages open out into cavities formed in one of either the casing body or the lid, and through which cavities the conduit screw passages permanently communicate with the enclosure defined by the casing. When the screwheads are in an untightened position with respect to the outer face of the lid, fluid communication is effected between said enclosure and the outside of the mechanism casing by way of fluid conduits, which comprise one of the cavities and one of the conduit screw passages.