Another success story here. Thanks everyone! My '98 Expedition had the ABS light come on, and replacing the wheel sensor did the trick.

To elaborate some, on our '98 Eddie Bauer version, I had to remove the bolt and then slide a metal clip rearward, then use a screw driver to pry the old sensor out. The old sensor had a bare metal cylinder that was magnetic. The new sensor from Advanced Auto was all plastic, but I could tell it had a magnet inside. It looked different but still fixed the problem (so far, as of a couple days). At first I didn't think it worked, but then I disconnected the negative of the battery and reconnected and that did the trick.