2018 Holden Colorado has leaks in the top near the brake light

Not every Colorado suffers this problem, but there are certainly a percentage that do. It’s a relatively common thing with this model and the first sign is a stain that develops on the roof lining in the rear seat just above the rear window. It’s caused by water entering the cabin through the high-mount brake light assembly.

The problem is caused by the light’s seals that fail over time, and the fix is to remove the light, clean the area around it and then seal it with panel sealer (or something similar) from the outside. If you’re fussy, you can replace the whole light assembly, but that won’t fix the failed seal, so you’ll still need to reseal the area where the light mounts.