The study of a thin, incompressible Newtonian fluid layer trapped between two almost parallel, sliding surfaces has been actively pursued in the last decades. This subject includes lubrication applications such as slider bearing or the sealing of non-pressurized fluids with rubber rotary shaft seals. In the present work we analyze the flow of lubricant fluid through the micro-gap of rotary lip seals. This study is carried out assuming that a “small-gap” parameter attains an extreme value in the Navier-Stokes equations. In particular, the effect of surface roughness, excentricity and centrifugal forces is analyzed using the technique. The precise meaning of small gap is achieved by the particular limit which, within the bounds of the hypotheses, predicts transport of lubricant through the sealed area by centrifugal instabilities. Numerical results obtained with the finite element method are presented.