Remove the master cylinder, pull it apart, follow the workshop manual, easy as.. make sure everything is sparkling clean, you don't want any little bit of dirt getting in there. after you remove the piston assembly you can shine a torch in there and you will be able to see if there has been any corrosion, contamination, scoring, etc. In my case it was just old seals that lost tension.
Brakes are better than they have ever been. Transfer case clutchpack decided to die shortly after as well, never ends.