Preheat the oven to 350°F and butter a deep 2.5-quart baking dish.
Bring a large pot of water to a boil, add the macaroni and vegetable oil and cook for about 7 minutes until partially tender. Drain well and return the macaroni to the pot.
Melt 8 tablespoons of butter and stir it into the cooked macaroni until evenly coated.
In a bowl, combine the shredded Muenster, mild cheddar, sharp cheddar and Monterey Jack cheeses.
Add 1 1/2 cups of the shredded cheese mixture to the macaroni, reserving the remaining 1/2 cup for topping.
Pour in the half-and-half, add the cubed Velveeta and gently fold in the beaten eggs.
Season with seasoning salt and ground pepper, then mix until well combined.
Transfer the mixture to the prepared baking dish and spread evenly.
Sprinkle the reserved shredded cheese over the top and dot with the remaining 1 tablespoon of butter.
Bake for 30 to 35 minutes, until golden and bubbly.