| If the shim has broken and fell out, then I doubt it'd cause seizure. It'd more than likely get chewed to little pieces!!
I don't think think this will be the case though. I'd guess it never had one in there in the first place. Possibly '96 specs allowed a bigger float? Not sure.
The bike I had in was just out of warranty but was sorted as it was deemed that it never had a shim in there in the first place. '96 is a long time ago though, so I think you'd struggle on that one.
Is the front sprocket showing any abnormal wear to one side more than the other? If not then the shaft float isn't affecting the chain line too much. Has the gear change been OK? If so, then the meshing up of the gear clusters isn't being affected.
"If it 'aint broke.......don't mess with it" might be in order here? It's not technically right, but if it's all working OK then is it worth a full rip down to shim that shaft up? Only you can answer that one, but I'd be inclined to leave it.............. | 
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