Season thighs with salt and pepper. Brown thighs in oil in a large skillet over medium-high heat, for about 2 minutes per side. Place browned thighs in the slow cooker. Add orange juice. Cover and cook on low for approximately 3 hours until thighs reach 180 degrees.
While chicken cooks, prepare sauce. Whisk together apricot preserves, horseradish, mustard and garlic. Set aside.
Place cooked chicken on a plate. Heat sauce in a microwave proof container or 1 quart saucepan until warmed. Spoon sauce over chicken. Serve.