It has not been long enough to know if the fluid is coming back or not, but the Motorcraft plugs are remarkably better than the Autolite AP104 plugs. There is absolutely no question that my truck is happier today than it was 2 weeks ago. Fuel mileage numbers are not in, but the seat of my pants says that the engine is much stronger and far smoother than it has been for about a year, since I put the Autolites in.