Would The Difference Engine itself, the SteampunkTrope Maker, count? I think it could if we consider the Engines, i.e. mechanical, steam-driven computers invented by Charles Babbage, to be the Phlebotinum in question. Otherwise, the story tries to have a fairly realistic take on steam power, e.g. a coal-driven automobile is shown to be realistically inefficient and consumes vast amounts of fuel to get anywhere. The Engines are what makes the story possible, and Babbage's perfection of the Analytical Engine is what splits off the story's universe form our own. For example, they are used to design the streamlined coal-driven cars, and they run the government databases that play an important part of the book's plot.
Would The Difference Engine itself, the Steampunk Trope Maker, count? I think it could if we consider the Engines, i.e. mechanical, steam-driven computers invented by Charles Babbage, to be the Phlebotinum in question. Otherwise, the story tries to have a fairly realistic take on steam power, e.g. a coal-driven automobile is shown to be realistically inefficient and consumes vast amounts of fuel to get anywhere. The Engines are what makes the story possible, and Babbage's perfection of the Analytical Engine is what splits off the story's universe form our own. For example, they are used to design the streamlined coal-driven cars, and they run the government databases that play an important part of the book's plot.