Add the mayo, buttermilk, vinegar, mustard, garlic powder, salt, pepper, Worcestershire, sugar, and MSG to a medium bowl and whisk to combine. Crumble the blue cheese and fold into the dressing. Cover or store in a jar in the refrigerator for at least 1 hour to allow the flavors to meld. Add additional salt and pepper to taste before serving. Add additional buttermilk if you'd like a thinner dressing. Will keep for 1 to 2 weeks.