Well. I let the system gravity drain 3 times before sealing it up and start the air bleed procedure, my TT has a bleeder on the slave and one on the passenger fender well. Followed the procedure found in the FSM and here on this forum and don't recall any issues. Just be sure to keep the reservoir filled at all times. Sounds like you have followed the proper procedures so I would start looking at replacing the slave cylinder. They are available at local parts house and relatively cheap. Good luck