6.2 liter LS valve problems??

[g356gear]

My sister has a 2007 Escalade Ext with the 400hp 6.2 LS motor. Last Friday the truck did a heavy shimmy shake and stopped dead on the hwy. Long story short, the dealer pulled the valve cover and discovered the engine had swallowed a valve into the motor. Dealer said this is a common problem with the 6.2 and that they will do a full longblock crate motor exchange. Apparently these motors have a "hardened" valve that has been breaking from being too hard to the point of being brittle. Truck has 53000 miles. Has anyone seen or heard of this problem? Dealer said it is a common and they don't even bother to repair the motors anymore, they just change them out.