Warped diff. housing?

[MrWizard]

Dealer says the leak in the rear of my 98 vert. is caused by a warped diffential half housing , it has 60k on it , how does this happen ? also it must be somewhat common as they are replacing it with the updated version...can anyone help?

 

[Mike Mercury]

are they replacing the entire carrier, or just updating to the new O-Ring seals?