Are you SURE there is an oil made today that will "sludge up" an engine? More likely, like my neighbor, pretends to do oil changes on his Mercedes, but just resets the service monitor. I've seen him do it a couple times already on his wife's GLA!
He sees the hood open on my E and asks what I'm doing. "Just checking the oil" I say. his reply, "On a Mercedes?" "No need for that."
I'll admit, I've never used any oil between changes, and even though it has the 2.0 Turbo, I don't notice any gasoline smell in the oil.
Short trip driving usually gets me about 34 MPG, and it runs as well as a V6.
I'm more impressed with this 2018 each time I get into it. It is just a pleasure to own and drive.
Now if I could only figure out how to make it park itself (it has that capability) I'd be done learning all the tech included in this one!