The Army is so short of spare parts for its helicopter fleet that it is spending tens of millions of dollars to overhaul old parts, the General Accounting Office reported. The study, requested by Sen. William V. Roth, Jr. (R-Del.), focused on the Corpus Christi, Tex., Army Depot, the largest of the eight depots where the service repairs about 20% of its 8,400 helicopters. The most common form of working around a parts shortage was to repair a worn part, rather than throw it away.