NEW YORK — Morgan Stanley posted its first quarterly loss ever Wednesday after taking an additional $5.7 billion write-down related to subprime mortgages. The investment bank also said it would sell a $5 billion stake to China Investment Corp., a sovereign wealth fund, to shore up its capital. The sale, which would give the Chinese government a stake of about 9.9 percent in one of Wall Street’s biggest investment banks, is the latest example of a foreign investor aiding a Western financial firm after the housing meltdown. Morgan Stanley’s fourth-quarter loss of $3.59 billion, or $3.61 a share, was a sharp drop from its year-earlier profit of $1.98 billion, or $1.87 a share. Analysts surveyed by Bloomberg News had expected a loss of 39 cents a share. With the second write-down, Morgan Stanley has lowered the value of its subprime holdings by $9.4 billion, one of the largest devaluations on Wall Street. In a statement, the bank’s chief executive, John Mack, said he took full responsibility and would forgo a bonus for 2007. ‘The write-down Morgan Stanley took this quarter is deeply disappointing – to me, to our colleagues, to our board and to our […]