Gtech model DM001. I have dismantled the GTech to access the gearbox. The nylon cog does not look too worn, but I noticed the drive shaft that connects the motor to the spindle via the belt drive appears to slip if the metal angled cog (the one that meshes with the nylon spindle cog) is held and the large belt drive cog is rotated (i.e. You can hold one end still and the other end will still rotate). Is this as designed to prevent damage to the motor or is this drive shaft broken? The fundamental problem is the brush heads do not rotate when in contact with the carpet. If the vacuum is tilted back so they are not in contact with the carpet such that there is no opposing force, they do rotate.