LONDON (MarketWatch) -- General Motors was downgraded to underperform from buy at Merrill Lynch, with the broker also cutting ArvinMeritor to underperform from neutral, Asbury Automotive to neutral from buy and Visteon to underperform from neutral. On GM, Merrill cut its price target to $7 from $28 and said the automaker needs a $15 billion capital infusion. "We believe there is potential downside in the stock below $7 and that bankruptcy is not impossible if the market continues to deteriorate and significant incremental capital is not raised," the broker said. ...