Brakes Locking

Open the bleeder screw to see if that caliper releases. If it does not, replace both calipers for even braking. If it does release, the next time crack the steel line open at the master cylinder. If the caliper releases there, suspect the brake fluid is contaminated with petroleum product. That will be a REAL expensive repair. If the caliper doesn't release from the master cylinder, suspect the rubber flex hose is coming apart inside and acting like a check valve for the brake fluid.

My guess is that fluid contamination isn't the problem because both calipers would typically be dragging at the same time.