Master Cylinder Failure

[Lockcuff]

Hello, after the last post about my 2010 calipers sticking nothing I could do would stop the dragging so I took the runner to the dealer and hey said the MC Pushrod was out of adjustment and they adjusted it and the brakes actually released. After driving roughly 500mi they started dragging again, so I adjusted the rod again myself and it seemed to release again. We drove about 100mi round trip last night and randomly about 10mis from home last night they started dragging again.
I have an appointment on Monday again at Toyota to re-check it, any ideas as to what is going on? I have another trip to take tomorrow and would love to drive the 4runner, I am gonna re-adjust the pushrod and see if it releases again. Could the piston be sticking and not returning and messing with the rod un-sticking it? Can the piston be pulled out from under the dash?
Thanks

 

[Maingear]

fluid needs to be changed every 3 years because it absorbes moisture from air that will pit and seize master cylinder piston.

Have you disassembled the calipers and made sure the pins that the pads slide on are in excellent shape?

If it is the master cylinder, I would not pay for new.. see car-parts.com
Not worth working on with the thousands of like new spares sitting on shelves.
There is a snap ring that holds the piston in, will make a mess, do exploritory surgery after swap is made on the bench, easier to clean mess there, or do it in the kitchen and make wife happy by showing her how handy you are!