Resolved - Thanks
The problem has been resolved with the help of the Shimano technical documents. Thanks to both of you for your feedback.
EDIT: For reference, the screw which is tightened to hold the shifter onto the hub seems to have been the culprit. When I took it all the way out, the threading was full of a thin spiral of metal, which was apparently carved out of the inside of the threading in the shifter. I cleaned both out and tried the screw again. It wouldn't go in perfectly straight but is holding the shifter on tight enough to cause it to function, if somewhat erratically.
Last edited by evanlong; 07-30-09 at 01:07 PM.
Reason: additional information