Apparatus and method for on-board lubrication of a paint pumping piston including a reservoir for lubricant and a lubricant dispensing mechanism for delivering a predetermined repeatable amount of lubricant upon manual actuation of the lubricant dispensing mechanism. In one embodiment, a section of tubing acts as the reservoir, and in another embodiment, the reservoir is formed by a transparent or translucent chamber located adjacent an aperture in a pump housing to enable visual inspection of the level of lubricant in the reservoir. A lubricant delivery piston is actuated by an extension thereof projecting through an aperture in the housing, and a lubricant discharge nozzle is located adjacent the paint pumping piston proximate a bushing supporting the paint pumping piston. A breather valve prevents a vacuum in the reservoir as the lubricant is dispensed.