Welcome back:
Most likely it is the rubber brake hose that runs to the caliper. Over time, the break down internally. Forcing fluid through is achieved, but when you release the brake pedal, there isn't enough pressure to return the fluid and the brake sticks.
Here is a simple way to test it. Safely lift and remove the wheel. Apply the brakes so the rotor will not turn and release the brake. When released, can you turn the rotor indicating the brake has released? If not do this.
Apply the brake again and try to turn the rotor. If you can't turn it, open the bleeder on the brake caliper which in turn will release the pressure on the brake pads. If you can then turn the rotor, replace that rubber brake hose.
Remember, if the caliper is sticking, the brake will get hotter than it should. Then, fluid begins to expand and forces the brake to lock.
Let me know what you find or if you have questions.
Take care,
Joe
Monday, April 22nd, 2019 AT 6:39 PM