Cook okra in 2 tbs. butter in a large skillet over medium-high heat, stirring constantly, until lightly browned. Set aside. Combining remaining quarter cup butter and flour in a large Dutch oven; cook over medium heat, stirring constantly, until roux is chololate colored (20 to 25 minutes). Stir in green onions, celery, and garlic; cook, stirring constantly, until vegetables are tender. Add okra, water, and next 6 ingredients. Bring to a boil; reduce heat, and simmer, uncovered, 2 hours, stirring occasionally. Peel and devein shrimp; add shrimp and crabmeat to okra mixture. Simmer an additional 10 minutes, stirring occasionally. Remove and discard bay leaf. Serve gumbo over rice. Add gumbo file', if desired.