I've had a couple fail, but I'd got some spares, so I simply replaced them. I kept the bad ones, as I had to disassemble them to see if they were repairable! I hate landfill!
The failure mode is either no light, dim light or flickering (usually before going off completely)
In each lamp there are 3 LEDs in series, and a nice constant current switching converter.
In all of the failures so far, the failure has been down to one of the LEDs going open circuit.
Repair is easy, using a current limited power supply, check each LED. The duff one reveals itself easily.
Removing the surface mount LED is easy enough, and it has a heatsink area on it's base. I removed a known good LED from on of the earlier faulty lamps, and replaced it, noting to check polarity, and adding a small dab of heatsink compound to the back of the LED.
The PCB on which the LED mounts to has a small copper area, which, in turn, forms a heatsink area with the aluminium body of the lamp. Ensure the LED is mounted so it's heatsink area is in good contact with the board, and, in turn , ensure the board has enough heatsink compound, and is seated tightly against the aluminium heatsink. On my lamps, the contact pressure is achieved by the lens clamping the board and LEDs together.
Note when soldering (or desoldering) a good LED, speed is of the essence. These devices are easily destroyed by heat. This is most likely the cause of the original failure.
Lamp showing two LEDs missing, the board and the aluminium heat sink.