ive had this problem before.....best thing you can do is get the piston out, sounds like a bit of grit was stopping the piston coming up all the way when you bled it when you over bled it the piston would have hit the obstruction and dragged it down, causing excess friction and stopping the piston coming back up.... Clamp the slaves ( with pads ) in a vice or with mole grips...., now remove lever blade and tpa.....then attach a syringe and bleed kit and force water in....this should force the master piston out the top of the lever body, you can then clean both and stretch the spring slightly