If you are talking about the inner felt peice between the glass and the frame, this is a "U channel", it fits in the frame, and the glass fits in it. It don't come out without separating the frame at the joint, and the window has to come out to do that.
The rubber peice on the outside of the lower pane comes right out. It does nothing but trim out the unit, but there are drain slots in the frame and the felt channel to let and water flow out rather than in. This could be dirty or clogged, and may be your problem.
itsa small window and they come out easy. It's caulked to the body around the front and top, you'll need to slice the caulk.
Then just unscrew the inner trim, and the window will fall out.