DETROIT (WKZO) -- General Motors officials believe that a lawsuit regarding rear-end problems with 2007-2008 Impalas should be thrown out.  Court papers show the automaker believes that it cannot be held liable for damages relating to vehicles produced before the new G.M. was created, after the old G.M. filed for bankruptcy in 2009.  The class-action suit, filed by a Pennsylvania Impala owner, claims that G.M. fixed rear-end problems on police versions of the vehicles but not on those owned by other drivers.  If the suit is successful, it could cost the automaker millions of dollars to replace parts and tires.