first, have you confirmed there is a hole in the clutch cable? if so, then yes, buy a new cable and o-ring for the cable.
secondly, check the cable at the primary case, check if it's loose...PO may have not tightened properly with cable replacement? ...wipe the oil off from around this area and ride the bike for a bit and see if any oil is seeping from it. if so, then the o-ring needs to be replaced, possibly the entire cable if the ferrell/cable connection has failed.
also, use a dremel and make a notch at an angle where the cable rest on the plastic, this will prevent the cable from rubbing on the plastic.