1. Rinse the scallops and pat dry with paper towels. With your fingers, peel away the small tab of tough connective tissue on the side of each scallop. In a bowl large enough to accommodate all the scallops, mix together the marinade ingredients. Add the scallops and toss to coat thoroughly. Leave to marinate in the refrigerator about 30 minutes. 2. Make the red onion marmalade: Cut the onions in half, then slice them thinly. Heat the olive oil in a large heavy bottomed saucepan and add the onions. Cook over medium heat until they begin to soften, about 10 minutes, then add the brown sugar and stir to coat. Season with salt and pepper. Continue cooking over medium heat, stirring frequently until the onions are beginning to turn golden brown, another 10-15 minutes. Add the vinegar and cook until it has completely evaporated, then add the red wine and repeat the process, stirring the onions frequently to prevent sticking and burning. When the red wine has evaporated, taste the marmalade and correct the seasoning. Remove from the heat and keep warm. (The marmalade may be made up to 1 day ahead.)