Abstract: A slack adjuster assembly for heavy-duty vehicles, the slack adjuster assembly comprising a slack adjuster and an inboard sealing assembly. The slack adjuster is disposed about and has an internal spline for receiving an external spline of an inboard end of a camshaft of a camshaft assembly of the heavy-duty vehicle. The internal spline has a radial clearance from the external spline. The inboard sealing assembly includes mechanical components that cooperate with the radial clearance to increase grease flow and distribution. The inboard sealing assembly is disposed over the inboard end of the camshaft and engages an inboard side of the slack adjuster to form a 360-degree seal about the inboard side.