You are on the right track. Replace the o ring and check the bore for a groove or trash with your pinky.
My trick for sealing leaky sheathed lines is to hose off the sheath with carb spray, apply weatherstrip adhesive and slide the shrink wrap over that and apply some heat to get it tight.
My trick for sealing leaky sheathed lines is to hose off the sheath with carb spray, apply weatherstrip adhesive and slide the shrink wrap over that and apply some heat to get it tight.