Change the brake fluid.
Brake fluid absorbs water even in a closed system like our cars.
It would be best to use a evacuation system. I have a OTC Fluid Evacuation? Brake Bleeding Tool from Summit.
Flush a couple of large container of brake fluid through the system.
I like dot 4
synthetic.
I put dot 5 in a 64 Plymouth for a friend at his request. A couple of weeks latter he came back and ask that I replace it with dot 4 because the brakes were spongy.
Change the fluid and the brake were good.
Air and water; the enemy of good brakes.
Eight years ago Mike brought his Cobra to me for general maintenance. I could not stop the car within a save distance. Bad brakes!
I changed the fluid and then I could lock up the tires. I was amazed at the difference.