Hydraulic reservoir cover seal, reservoir with such a cover, and methods of assembling such a cover

The sealing unit has a cap molded to a skirt (12) including a cavity (13). A sealing lip (19) is crushed between a lower side of the cap and an upper side (17) of the skirt. An electric circuit e.g. reed switch circuit, to detect level of liquid in a reservoir is placed in the cavity. The lip follows circumference of an orifice (18) situated on the upper side of the skirt. Independent claims are also included for the following: (A) a hydraulic reservoir for a motor vehicle (B) a method of assembling a sealing unit.