1998 Lincoln Navigator, brake light on, filled fluid resevoir light went off, next day came back on. Brakes spongy. Replaced pads front and rear at 87,000 miles, currently at 111,000

Not completely sure here as i cannot see it but i would hazard a guess and say that the master cylinder needs changing ,but check the fluid level first and if low again then you have a fluid leak but where ?? could be a caliper seal or the master cylinder leaking out of the rear seal and its being sucked into the air intake via the servo vacumn pipe?? could even be a flexible pipe split or a damaged brake pipe ,Evan if pads on metal you should still have a hard pedal ,Have a good look around to see if its leaking first

30k is reccomended brake replacement. If it goes to far it will cost big money