<p>Is there any simple way of creating tappered thread in OpenSCAD? I need something like 10 mm in diameter at the end, 9 at the top and the height of 10 mm.</p>

If you are able to remove the gear, as I suspect you can, a useful tool is the file card. It resembles a flat hair brush but the bristles are short wire, very stiff. In traditional use, it removes metal shavings from conventional metal files. It will easily remove plastic from between the gear teeth. If you are unable to remove the gear, but can access a portion of the exposed teeth, a suitably named dental pick can remove slowly the clogged material.
Cooking the gear may not cause a fire, but could carbonize the plastic onto the teeth, perhaps creating a greater problem.