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Perhaps some steps of this could be used to repair the original tuners....
http://www.frets.com/FretsPages/Luthier/Technique/Mandolin/TunerRepair/F4GearFix/f4gearfix.html

Look on the bottom of each of the Stewmac tuner pages. You'll see a drawing with the dimensions on them.

especially the ability to define a search by price levels, for instance show me only mandolins that have a listed price of over, under, or between $x