I come across a lot of them that just need to be snapped back on. Sometimes you get lucky and can fix them without taking them completely apart. As for the center vent being loose, There's a small square rubber piece that the vents rub up against and keeps tension on them. That rubber piece either shrinks or gets worn down over time. I put a shim behind it on mine and it fixed the problem of them flopping down. You'll have take the center vent apart to repair them though.
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Woody
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