The LEDs themselves are very reliable. From what I’ve seen here, most people lose a bunch of them at once. This makes me wonder if it is a circuitry problem rather than an LED failure. The only LED failure that would cause a whole row to go out at once would be if they are hooked up in series and that isn’t usually the way one wires LEDs.
Anyway, you can buy individual LEDs. They vary in brightness so if one was to replace an LED, you’d want to match the color and brightness. If it is a circuit problem, replacing an LED isn’t likely to fix the problem.
I don’t know if the assembly can be disassembled to allow one to get to the LEDs or the supporting circuit boards. If the overall housing is glued it might be nearly impossible to take it apart without destroying the overall assembly.
If anyone has one that has been replaced outside of warranty, and has the old part, I’d love to see if it can be repaired.