Combine vinegars, salt, pepper, cloves, bay leaves and mustard seeds in a large bowl. Place roast in bowl; cover and refrigerate overnight, turning once.
Place roast and marinade in slow cooker and cook on HIGH for 6 hours or LOW for 8 hours.
Remove roast to a platter and keep warm. Strain liquid from slow cooker. Stir in crushed gingersnaps until well blended. Slice roast and serve with mashed potatoes and salad, if desired. Makes 10 servings.