Damn the curse of abundance!
That sounds like you have some corrosion or other contamination inside the switch mechanism. Replacement will likely be the only thing to get it like new again, unless you're into a component-level teardown and cleaning of your laptop keyboard (which could easily make things worse!).
My best thought for a quick fix: buy or borrow a cheap USB keyboard.
I thought about getting an external keyboard. But, I rather like the look of a sleek black Apple keyboard with a single glowing white hole in the middle where the U key used to be. It will make me feel extra stylish when I go into Starbucks next time.
Sounds like a great plan!