After a couple of days of SLAMming and not passing the OCLT, despite crystal clear water and no CC, we decided to look behind the light. Bingo. It was quite gross behind there.
We brush the nook and left the light out for a couple of hours with water at the SLAM level. Then my husband spent a good hour fighting the light to get it back in, but it's in there now.
And now that's done, I'm wondering if we left the nook exposed to chlorine long enough. Don't even want to tell my husband the light has to come back out. If it has to come back out, it will be after the long weekend with a house full of guests.