Interesting drum brake problem

Drum brakes? Does it have the right master cylinder? Both wells should be the same size.

I'm adding my 2¢ to those who are recommending new hoses. Look for crimps in the steel lines along the driver side rocker panel area and across the top of the rear axle housing. You'll need to bleed the brakes; RR, LR, RF, LF. Using a different sequence can cause you to chase an air bubble in the lines.

FWIW: The self-adjusters in the brakes will not loosen a brake that is set to tight. It will, when working properly, tighten a loose brake. To use the self-adjusters, locate a large open area where contact with other things is minimized. Back the car up to approximately 15 mph. Slam on the brakes hard. Drive forward about two car lengths and stop to evaluate adjustment. Repeat as necessary. If no improvement noted in three repetitions, something other than brake adjustment is wrong. For this to work properly, the brake shoes must be making contact with the drum when the brakes are applied.