With the lens off the camera, just turn the focus ring. An AF lens should have very low or no resistance to turning, and the same effort through its range. You can also turn the AF drive screw with a common screwdriver to see if that mechanism is dragging.
If it was me, I would not bother taking it apart unless you're really adventurous. AF zooms are complicated, and the focus mechanism is probably hidden under everything. You can easily find a lens with similar specs on eBay for $30-50, possibly with a free film camera attached.
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