The article notes that in order to more accurately predict the reliability of connections, it is necessary to investigate the influence on leaks not only of the geometric dimensions of the mating elements, but also of other factors. In particular, leaks in the sealing units are affected by the actual operating temperature and the aggressiveness of the hydraulic fluid. It is particularly noted that the tightness of the sealing joint is significantly affected by the amount of surface roughness of the parts in contact with the sealing ele-ment. To completely overlap the microchannels formed by protrusions and depressions on the sealing sur-face, it is necessary to create increased stresses in the sealer in the contact zone, which negatively affects its service life. The micrometer studies of the sealing components carried out earlier showed that the actual roughness of the surfaces of the sealed parts in contact with the rubber rings turned out to be significantly higher than required by the standard. Theoretical studies based on numerical modeling using an original finite element calculation program have shown that the first period of the function of the contact sealing joint is characterized by a constant contact area and the absence of leaks through the joint. A feature of the second period is a gradual decrease in the contact area due to the separation from the surface of the counterbody of the relaxation microrelief sealer formed in the boundary array. The wedging effect of hy-draulic fluid penetrating into the microrelief cavities leads at a certain stage to complete separation of the sealer and counterbody surfaces, elimination of the ability of the joint to self-seal and complete exhaustion of the resource. The article concludes that a more appropriate criterion for the exhaustion of the connec-tion resource in comparison with the criterion of limiting stresses is the time of the beginning of the for-mation of microchannels in the boundary array of the sealer.