They shipped the stuff to contractors for repairs in 2004. But the Army doesn't demand reciepts.
The Government Accountability Office added up all the missing parts -- which probably took a while with no reciepts. The GAO came up with that $68 million figure.
“Although the (Defense Department) policy requires the military services to confirm receipt of all assets shipped to contractors, the Army is not consistently recording shipment receipts in its inventory management systems.” -- Government Accountability Office (GAO) Report
The Army's not alone. The GAO's found similar accounting problems with the Navy and Air Force.