My old Harley's cables respond well to the old Ziploc bag with synthetic oil trick... disconnect cable at highest point, poke end through bottom corner of bag, tape bag to cable tightly with electrical tape, put about a half cup of oil in bag, zip bag closed, tape bag to something to keep it elevated overnight. Oil will migrate to the lowest end.
I take no responsibility if your engine sounds like a V-Twin when you fire her up!