General Motors (GM.N) seeking advice from investment banks shows it is taking an attempt by Fiat Chrysler Automobiles (FCA) (FCHA.MI) (FCAU.N) to force a merger with its larger U.S. rival seriously, analysts and traders said. GM openly rebuffed a merger proposal from the Italian-American carmaker earlier this year and CEO Mary Barra said last week she had no interest in a tie up.