DVD tracking

I've repaired a few CD players previously. Most of the time the problem was that the rail upon which slid the lens would get sticky and dirty, causing tracking errors. Clean it, put on some new grease - problem solved. A friend of mine was having problems with his DVD player and it sounded like a similar problem. When I took it apart and removed the drive system, I noticed that the gear that goes between the tracking motor and the comb-like flat gear on the laser assembly is actually two thin gears, one atop the other, with a spring between them. Can anyone tell me the purpose of this? Right now, the teeth on those two gears don't line up vertically. The problem I'm seeing is that you can only move the laser ass'y one tooth at a time, instead of being able to run it up and down the rail smoothly. And I think it's because the teeth on that gear aren't aligned. Any help/suggestions would be appreciated.