I've tried looking all over for a solution, but I've yet to find a solution that matches my situation. The cover I have (I think) is supposed to turn so the hole is downwards so you can remove the screw to remove the cap. However, this unit seems to be (somehow) installed upside-down. The cap can rotate easily from the 12 o'clock to the 3 o'clock, but there's a rim inside that's mostly covering the screw inside. I can also turn the cap (with some effort) from 12 o'clock to 10 o'clock but it sounds like something is cracking or grinding when I do.
I also tried removing the screw despite the metal rim inside, but it just loosened until it was pressing against that rim and wouldn't come out any more.
In case anyone is wondering, I'm trying to remove it because I think there's leaking happening behind there.