Yes if you never saw any leaks from the cables or anywhere the chances are very likely that your slave cylinder o-ring has called it a day. If it were me I would pull the slave cylinder off and check it out, replace the o-ring with a good viton o-ring and bleed the system with some new mineral fluid. You bleed it from the bottom up. It's like bleeding brakes you need a syringe with 6mm id tube to go over the little nipple and as you crack it you slowly push the new oil through. You might have to do it a few times to get all the air out (I did) and you can see little bubbles escaping the top reservoir. It is good to have someone help you.