I recently acquired a 1981 Spider 2000 and have about 300 miles into it. Last week I threw it over into reverse and the shift lever spun from the normal 6 o'clock around to 3 o'clock. I straightened it out and got it into gear, but from that moment the shifter is able to spin 90+ degrees while shifting between gears. Quasi-normal shifting is still possible if the shift-lever is held in line at 6 o'clock (like with a clenched fist). A peek under the center-console revealed why...

Neither the shift-lever nor the shaft looks particularly worn (though quite dirty), and the edges of the groove of the shaft are still quite sharp. My first inkling is to replace the whole shift-lever assembly and boot, but not the shaft. it's a used car and I have no idea what's happened up to this point- I haven't dug in from below, so I don't know what may (or may not) be there...
Here's a look at the offending behavior (.mov video 12M):
http://trentland.com/misc/fiatshifter.mov
Does this look instantly familiar to anyone? Am I barking up the right tree with the shift-lever replacement?
Edit: Is is possible that the entire "donut" around the shift-lever could be missing?!?!
regards,
trent