* TSX down 139.75 points, or 0.92 percent, at 14,980.79 * Nine of the 10 main index sectors decline * Valeant shares jump after ValueAct executive to join board By John Tilak TORONTO, Sept 25 (Reuters) - Canada's main stock index dropped for a fifth straight session on Thursday, nearing a three-month low, as sluggish U.S. economic data weighed on sentiment. Market volatility shot up and commodity prices remained choppy. A decline in the price of bullion sent gold-mining shares lower, offsetting a gain in Valeant Pharmaceuticals International Inc. Data showed orders for long-lasting U.S. manufactured goods in August recorded their biggest drop on record as aircraft orders fell back after jumping in July. Stock prices in the Toronto equity market have run ahead of fundamentals, said John Ing, president of Maison Placements Canada. "The action of late has been very volatile. We have been ripe for a pullback," he added. "The market has been overbought, has been overvalued. It's long overdue." The Toronto Stock Exchange's S&P/TSX composite index was down 139.75 points, or 0.92 percent, at 14,980.79. Nine of the 10 main sectors on the index were in the red. Financials, the index's most heavily weighted sector, dropped 1.1 percent. Toronto-Dominion Bank shed 1.6 percent to C$55.52, and Bank of Nova Scotia lost 1.5 percent to C$69.06. Shares of energy producers gave back 1.4 percent. Canadian Natural Resources Ltd declined 1 percent to C$43.68, and Suncor Energy Inc fell 0.9 percent to C$40.50. Valeant said it had named the head of a top shareholder, ValueAct Capital, to its board of directors and vowed to continue with its hostile takeover attempt on Botox maker Allergan Inc. Valeant shares jumped 2.7 percent to C$141.04, helping keep the healthcare sector in positive territory. ($1=$1.11 Canadian) (Editing by Peter Galloway)