Cook pasta according to package directions. There will be a few extra shells which is good since some always split or break apart.Meanwhile, in a small skillet, saute green pepper in 1 tablespoon butter until tender; set aside.
In a large bowl, combine the crab, shrimp, egg, 2 cups of mozzarella cheese, mayonnaise, 6 tablespoons milk, 1 1/2 tablespoons seafood seasoning, pepper and green pepper.
Drain and rinse pasta; stuff each shell with 1 rounded tablespoon of seafood mixture. Place in a 13-in. x 9-in. baking dish sprayed liberally with nonstick spray.
In a saucepan, melt remaining butter over medium heat. Whisk in flour and coarsely ground pepper; gradually whisk in remaining milk. Bring to a boil; cook and stir for 2 minutes or until thickened. Stir in Parmesan cheese and remaining mozzerella cheese.
Pour over stuffed shells. Sprinkle with remaining seafood seasoning. Bake, uncovered, at 350° for 30-35 minutes or until bubbly.