A small ball bearing or even a Torrington needle bearing would stabilize the top of the quill a lot more effectively than a piece of shim stock and it would be a pretty simple matter to support it on the outside with J-B Weld or something similar. It would outlast a shim by many years, also.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!