Back in the dark ages when I was a bodyman the primary causes of the symptom you describe were two: One is as Bill noted, the hinges are worn and need to be replaced. Two, and by far the most common, oil. Lubricate the hinges and often magic happens. I can't tell you how many times "sprung" or "worn out" hinges were "fixed" by a few drops of oil. Don't even try to align your body panels until the hinge problem is fixed.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.