General Motors Korea says it'll be shutting down one of its four car assembly plants by the end of May -- the one in Gunsan -- due to a plunge in local sales.br The Gunsan plant is the smallest of GM's local facilities.... and employs 15-hundred people.br The automaker saw its sales in Korea fall more than 26 percent last year.br Exports were also down 6 percent, and they account for the lion's share of sales.br GM Korea says the drop in demand could be because of high per-unit manufacturing costs and low productivity at underutilized assembly plants. br The company also hinted at further restructuring, saying that it may close more of its money-losing operations in Korea.