Brake fluid down in Master Cylinder but do not see any leaks.?

Sounds like a "stuck" caliper piston. Many Chrysler products used "phenolic" pistons in the calipers which were notorious for seizing in the caliper. Replacement pistons are usually made of steel. With the piston seized heat builds up and ruins the seals in the caliper.

You could have a blown master cylinder that is leaking from the back and into the booster area. Take the cylinder loose from the booster and see if there is fluid in that cavity. Sounds like a massive leak. Look at the rubber hoses and metal lines. The reason you cannot pump up the brakes is because the leak is allowing air to re-enter the system so that pressure cannot build up.

Fluid is going somewhere and should become apparent soon!

For the fluid problem it has to be leaking somewhere if you have to keep adding fluid. If it was leaking by the vacuum brake booster then it would be running down the front of it. Those are pretty much sealed to hold the vacuum, unless it's damaged somehow. Your front wheel brake cylinder may need replaced if it's sticking or hard to push the peddle and has that 'give' effect to it. Check all 4 wheel brake calipers for leakage. One of the brake lines may have a pin hole in it. The lines to the rear wheels run along the inside of the frame under the vehicle to the rear, then there's a junction to the other rear wheel.

I think the caliper is bad, or stuck, but just bleed all 4 brakes again and see if the pedal gets better

definite seems such as you enable it get too low on fluid and sucked some air. are you making use of two guy hand bleed technique or a one guy bleeder set-up? destructive guy's one guy bleeder is rapid and uncomplicated to make. right this is how. 12 inches or so of three/8 od gasoline line and 20oz bottle sparkling and empty be helpful whilst hose is linked to bleeder valve it reaches all the thank you to backside of bottle. connect gasoline line to bleeder valve and open valve a million/2 turn pump brakes slowly. each 4-5 pumps examine fluid point it is going to pump out rapid. what occurs is once you enable off brake it sucks a small volume of fluid from bottle into hose by using hoover often 15-20 pumps according to wheel is sturdy to thoroughly purge the lines. be helpful to tighten valve in the previous removing bleeder assembly or you will enable air in back.

If you bled the lines then the fluid you put in went to those line if. How did you bleed the lines? Did you put the brake petal to the floor an hold it for 1 second to bake shir that there was no air in the lines.if not that could have to do with your problem.