I did brakes recently, decided to buy new rotors and pads, realize that the slide pins are seized and the little boots are torn on one side and that caliper is probably toast, get everything put back together and it’s working for now. Try to bleed the brakes since the fluid looks like mud and the car has “speed bleeders” with check valves in them instead of little holes. The check valves are also seized because someone left the little rubber caps off so no fluid comes out until the bleeder screw is completely removed. I just let them gravity bleed for a minute and put them back in. I bought new bleeders so I can replace the fluid, probably should have just ordered calipers at this point.