As far as I know, the reason for the plastic gears is to restrict the life of the shredder so the guy with the broken M/C will go and spend his money on another one.
This is what manufactures call "built in obselescence" it's a ploy to get more money out of the public as most people will not go to the bother of having a small appliance repaired
This is down to the fact that we are all guilty of being wastefull and manufacturing companies seem to encourage this attitude instead of making products with built in quality to last a good period of time
I myself have a LERVIA KH 4402 Shredder that has not done the justice for the price that I paid and I am looking for a gear that will fit with the motor shaft from other types of appliances that maybe I can modify to fit rather than throw the whole unit away
Brian
January 2010