72RATCAMARO

So I have replaced both slave and master cyl and still losing fluid and have no idea where. it has a speed bleeder with an extension. the extension spins inside the attachment connection i guess you could call it. what could be leaking? its getting kinda frustrating as i am selling my truck and want to make sure the new owner gets a truck that is running right and ready to go. so any help would be greatly appreciated. i am seriously considering just putting my normal bleeder back on. HELP