To make sauce, melt butter and add flour, garlic, onion juice, Worcestershire sauce, celery seed and liquid. Add mushrooms and shrimp. Cook until thickened. Put oysters in saucepan and simmer just until edges curl. Drain. Put oysters on cleaned oyster shells. Cover each with sauce mixture. Sprinkle each with cheese. Place on tray covered with rock salt. Broil for about 5 minutes or until bubbly.