Small Engines (Lawn Mowers, etc.): Toro 20064 - Self Propelled drive stopped working, wheel gears, drive wheels

Question
I have a 2008 Toro model 20064 recycler lawn mower on which the self propel drive has stopped working.  Two weeks ago, my wife reported that it started to make some noise, and now it starts to engage - the wheels spin for a short second or two - and then it stops.  I have cleaned out the housing that protects the belt (lots of old dry grass was wedged in there), as well as checked the general condition of the belt (it looks okay).   I have also lubricated the system via the owners' manual, but no improvement.  

What other things should I check before bringing it in for repair?  Thanks!!

Answer
The transaxles on these fail from time to time.  The gearbox gets full of dirt and grass when the seals and bushings start to fail and the pinion won't contact the ring gear any longer.  This might be the problem and would require replacing the entire transaxle.  The wheel gears could also be stripped.  Pull the drive wheels and you will see the gears and can check that they're engaging and they are keyed to the axle.  Thanks, PK.