I removed mine and re-bent the little springs that pop it up. I was going to post a how-to on this, but never got around to it. Just look carefully at the assembly while the roof panel is open. There are screws along the front that you take out and then the whole thing comes out. On the bench, play around with the flap to see how the springs work, very hard to describe. I too was going to add springs, but after putzing around, you can just "wind" the originals up a bit more by bending them to increase the tension to compensate for "tired" springs.

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1986 560SL
2002 Toyota Camry
1993 Lexus