Are you sure it is a cassette and not a freewheel?
I don't know if Shimano still makes freewheels, but with the wobbling and different size tool needed, it sounds like a freewheel to me.... when you hold the wheel and spin the cogs, do the splines where the tool is supposed to engage move?
If the splines move with the cogs, it is a cassette. If they stay with the wheel while the cogs move, you have a freewheel.
EDIT: Never mind, I just read the Falcon reference...
Good luck on the repair... but the wobble, is nothing to be overly concerned with.
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Last edited by Little Darwin; 09-05-08 at 01:58 PM.