In a small bowl mix salt, pepper, oregano and garlic until thoroughly combined. Rub mixture evenly over top and sides of pork; let stand at room temperature for 30 minutes. In medium size skillet, heat oil over medium heat. Place pork in skillet and brown on all sides. Place chicken stock, bay leaf, and pork into a crock pot; and cook on high for 3 hours. Pork should reach an internal temperature of at least 145°F. Discard bay leaf; leaving pork and any remaining chicken stock in crock pot. Using two forks, carefully shred pork, add barbecue sauce, and toss to coat. Place shredded pork on bottom half of each bun and close sandwiches with top half of bun.