See photo. I'm not even sure I'm using the right terminology, because I don't know the name of this type of window.
It's very hard to get these areas clean from the inside. Is it truly necessary to remove the screen, open the window, wet, and spray out this funk?
The ridges that make the seal just seem to fight against anything being removed from the area.
If you know the type of window and a better way to ask this question, I welcome new title/clarity suggestions!