96/97 dodge dakota falling brake pedal

Thought this was open and shut case .customer reported falling pedal and brake light coming on and off. I checked the master cylinder, and it was leaking out of the back down the brake booster. I figured the leak would explain the pedal drop,and the brake light coming on because of the pressure drop. I replaced brake master cylinder. The leak stopped,but the light and dropping pedal persisted even after thorough bleeding of all 4 brakes...in order farthest to closest to the master. To top it off finding parts is rough with this vehicle because it's what I call "a frankinvehicle" some parts 96 some 97 in a 96 truck.and this... I know this isn't a technical type question but I need some guideance please. I know somewhere in your vast sea of experience someone has to have this answer.

If you have checked all the pipe work very carefully for a leak under pressure, the if we assume the new master cylinder is good then you have to go round each wheel in turn, strange as may seem a sticking on its slides or seized caliper can cause a sinking spongy pedal. You can eliminate each wheel in turn by clamping off the flex hoses one at a time and trying the pedal,
One quick test on the master cylinder is to top the fluid up until it is almot overflowing and watch if the fluid rises when the pedal is pressed.
If after you want 100% certainty that the master cylinder is okay screw a bleed nipple into each of the outlets and trying the pedal.

Thank you for that Andy. Found out it was a sticking caliper. Who of thunk it.lol thanks again.

Glad you found it! Would you mind please editing the title to add FIXED?