Seventy employees at Gibbs Die Casting Corp. in Henderson, Ky., have been asked by the company to extend their holiday vacation one week because of a lack of work. Sheri Pfingston, a Gibbs human resource generalist, said the 70 work in the die casting plant. Their work is driven by the automotive industry, some of whose plants currently are closed, she said. Meanwhile, 700 other Gibbs employees are…