I have two Big Haulers, 4-6-0's with only about 1 hour of track time on each.   Both have developed a slip in the (at least it appers to be) the worm gear.   I can hear it spinning but it is not engages the wheels.  I have not taken it apart yet and don't know if i should.  I hate to have to send them to the factory but if the fix is not simple I will.  Any suggestions???