How many miles covered since January 2011?
I have a theory that if the kingpin bushes are not reamed with care, it's possible to create a bit too much play right from the start. It's early to have had them changed after two years anyway. What was the mileage in January 2011? Either the new bushes were not reamed accurately, or you've been driving on roads which have generated a lot of abrasive dust.
Have a close look at the state of the pins inside the rebound springs and see if a good greasing on the bottom nipple helps.
