General Motors Co. is seeking to dismiss a lawsuit over a suspension problem on more than 400,000 Chevrolet Impalas from the 2007 and 2008 model years, saying it should not be responsible for repairs because the flaw predated its bankruptcy. The lawsuit, filed on June 29 by Donna Trusky of Blakely, Penn., contended that her Impala suffered from faulty rear spindle rods, causing her rear tires to wear out after just 6,000 miles.