i was very surprised to find this. it's a curado 101D.
(http://alantani.com/gallery/0/1_02_01_09_12_41_11_0.jpeg)
(http://alantani.com/gallery/0/1_02_01_09_12_41_13_1.jpeg)
turning the handle, it felt like the gear teeth were broken. sure enough, they were.
(http://alantani.com/gallery/0/1_02_01_09_12_41_15_2.jpeg)
(http://alantani.com/gallery/0/1_02_01_09_12_41_17_3.jpeg)
i called shimano and they were aware of the problem. here's the answer.
(http://alantani.com/gallery/0/1_02_01_09_12_41_19_4.jpeg)
(http://alantani.com/gallery/0/1_02_01_09_12_41_21_5.jpeg)
it worked beautifully. if you have one of these, you will probably need to upgrade eventually.