Backlight on keyboard dying one-by-one?

Here's a slow, boring VIDEO of both a key and LED replacement being performed on a mechanical keyboard.

So, you could look for replacement LEDs to match what you have in your keyboard, de-solder the malfunctioning ones, and solder in the replacements. If you're handy it shouldn't be too bad of a job. Here's a SITE with replacement LEDs and key switches. Not sure if they match what you're looking for, but it never hurts to look.