Are you sure it's the gears and not the motor? The motors on these drills fail a lot with the magnets coming loose/breaking up and jamming the armature rotor.
Also you should not be able to rotate the gears by moving the chuck anyway. This is normal as it has a locking action to enable easy tightening/loosening of the chuck jaws. I bet your fault is the all too common motor magnet issue. See:
http://www.howtomendit.com/answers.php?id=172558
and:
http://tinyurl.com/3ldfx5 (amazon buyer reviews)
If it is this issue, I suggest you contact Bosch and complain like mad till they agree to do something. They must clearly know about this notorious issue and even if outside warranty, they should fix it FOC as it is a very bad design issue on a drill which is otherwise superb.
good luck
Drillman, October 2008
