Tires: AWD and replacing only 1 tire, mercury milan, michelins

Question
I have a Mercury Milan 2007 AWD. It has Michelin HX MXM4 P225/50R17. The Tread life is 6/32nds. with 24K miles. New specs are 10/32nds. One tire was ran flat a destroyed. The questions is do I buy 1 or 2? Do I run the new on Front? Or do I need to buy 4 new? How will this effect the driveline?

Answer
Rob,

 It's not surprising that the Michelins have that much wear in only 24K miles.  You have two options with the AWD: 1) If possible find a used tire with the same 32nds  2) Purchase 4 new tires in order to keep the 32nds the same.   Look into Toyo or Bridgestone and I feel you will be pleasantly surprised compared to the Michelin.