Problems! + DOT 3 Synthetic Brake Fluid Yay or Nay? Greetings! Having brake problems with my 2002 Liberty 165k miles 4WD V6 ABS. Drums in rear. I replaced both front brake lines after Right Front blew out at caliper end. (It was rust rotted where rubber hose meets the metal tube) Calipers work good. I was using DOT 3+ brake fluid with no issues. When the brake hose broke, all the fluid left the reservoir, so I had to refill & bleed but I switched to DOT 3 Synthetic. I used a compressor powered vacuum bleeder that worked great last flush. I bled brakes per factory instructions. I could actually see the air being bled out. After bleeding with reservoir full. The pedal felt great with the engine off. After starting the engine I pumped the brakes. ...After a few pumps, the pedal went to the floor and got stuck there. I shut the engine -the pedal eventually back came up. Afterwards the pedal is spongy soft and braking is poor. No Brake Light indicator. (I've never seen this before) I dont know how old the Master cylinder is so I'm ready to change it being its age is unknown and pedal hit the floor. Questions 1) Do I need to bench bleed the old master cylinder or is the vacuum bleeding the way to go. Do I need to bench bleed the new master cylinder? 2) Is DOT 3 Synthetic the problem? 3) Does this sound like a bad Master Cylinder? ("pedal went to the floor and got stuck") Thanks you your input!