Bring a large pot of salted water to a boil. Add potatoes, cook until tender but still firm, about 15 minutes. Drain, and transfer to a large bowl.Place eggs in a saucepan, and cover completely with cold water. Bring water to a boil. Cover, remove from heat, and let eggs stand in hot water for 10 to 12 minutes. Remove from hot water, and cool. Peel, chop, and add to potatoes.In a small bowl, combine lemon juice, oil, sugar, seasoned salt, Worcestershire sauce, mustard powder and black pepper, mix well. Blend in mayonnaise. Pour lemon dressing over potatoes, and stir to coat.Mix in green onions, celery, and parsley. Refrigerate for at least 2 hours before serving.