Yep, just the brush. I made the initial shape with a 100% opacity brush, then lowered the opacity to modify it. Have you Alt-clicked on the mask to see it in black-and-white?
Yes, it will be a different levels layer for each reflection I'm afraid.
You can tell that by looking at which sliders have moved on the levels layer - either the ones at the white end, or the ones at the black end.