On the rare occasion of a broken clip, you can get this Replacement Clip Kit that includes a replacement clip and metal dowel.
To replace the clip: Turn the light unit on it's side on the edge of a flat surface so that the red clip is on its side. With a small hammer and small punch carefully tap the dowel that holds the clip to the unit down and out. This may take some time and care but it will slide out.
To install new clip, reverse the process.