Giving thought to purevw's response about a piston seizing in a brake caliper. 168K miles is quite a few. If it were mine, I'd remove the caliper and note where the piston was. I'd probably mark it with a sharpie. Then I'd carefully compress the piston like I would for new pads. Yours might not go in much. Next, I'd have my wife slowly press the brake pedal, to see if the piston moves up to the line I marked. "hint, very slowly" I would not want the piston to come out and make a fluid mess on the floor!. I would compress it again and repeat, making sure each way is smooth and like normal. After a few cycles, reassemble and go for a test drive. If it still acted like a skid steer, I'd replace the caliper(s), bleed the lines and hope you got it fixed.