Also, if you take the heads out (undo the two setscrews holding the little bar it slides on and pull the two ribbon connectors, making note of which one goes where) and look at them from the front, you should see a spring inside. It's likely that spring got stretched a bit. There are three pairs of little indentations where the spring hooks, each a little farther apart. If you move the spring to one of those sets, it increases the tension, and then the head should close like normal.
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