The aluminum trim is set into the rubber seal before installing the glass. It cannot be removed separately without damaging it. The window is easy to remove. Carefully roll the rubber seal upward and outward while applying gentle pressure from the inside. I have done this job for the same reason - rust under the rubber seal. In fact, lifting the aluminum trim won't reveal anything. The rust is coming from the steel panel under the rubber seal.

To reinstall, lube the seal, insert two cords into the groove in the rubber seal, set the window over the opening and have a helper apply gentle pressure, then pull the cords to roll the seal lip over the flange.