Advised to get ball joints replaced!!

I did some research on this and it seems that the ball joints are "designed for the entire life of the vehicle.
See this document which advises that mechanics often check for axial play (up and down) which is not appropriate on the Sprinter which would only be checked for lateral play.

Here is the Sprinter Source article about checking the ball joints.
Here is a long forum post about changing the ball joints.

I need to check the ball joints again to confirm if the Mercedes Dealership tested them correctly!

HERE the ball joints are $28.59 each from Micks Garage, probably plus postage