Welcome to smoother shifting, a quieter drive train, and greater ease of finding neutral.  Engine oil is designed for 1 thing.  Engines!  Your primary/clutch assembly has different lubrication requirements and we only trust Spectro Primary chaincase oil.  It is a full synthetic lubricant that is specifically formulated for your Harley's primary chain case.  This sheer stable petroleum is designed to withstand the punishment of high loads, and contains special polymers to provide exceptional clutch engagement and temperature stability. Meets full OEM requirements, and should be used according to manufacturer’s instructions. Formulated specifically for Harley® Sportster and Big Twin applications. Low drag, low friction loss SAE 85w viscosity eliminates clutch “drag” and slipping.

This kits includes everything that you need to change your primary fluid.  The oil, Derby cover o-ring, and a new drain plug o-ring.