Red Line V-Twin Primary Case Oil Features Red Line V-Twin Primary Case Oil offers improved wet-clutch operation Developed for 1984-to-present V-Twin American motorcycle engines Improves clutch operation while reducing wear and temperature Where most synthetics are too slippery for clutch operation, this friction-balanced product is balanced to provide less slip, smoother operation, and helps to apply more power in modified engines For use in the primary chaincase with wet-diaphragm spring clutches