Wash chicken and giblets; pat dry. Season chicken with salt and pepper. Sprinkle half of garlic and oregano inside cavity of chicken. Melt butter in frying pan and brown chicken. Transfer to crock pot. Sprinkle with remaining oregano and garlic.
Add sherry to frying pan, stir to loosen brown bits. Pour into crock pot. Cover, cook over low (200 degrees) for 8 hours. Add lemon juice last hour. Transfer chicken to cutting board. Skim fat from juices and pour to a serving bowl. Carve chicken. Serve with juices over chicken.