If the cone of the woofer has seized solid (common problem), it can usually be repaired with a little skill. Before the new forum took over the old forums URL you could look up guidance and tips for repairing your woofer. Several threads in the old (archived) forum discussed and showed how. Now you will be lucky if google comes up with anything usable.
But, basically, it’s a matter of manipulating the magnet and the pole piece.