The massive failure of the Oroville Dam’s main spillway in February involved two dozen potential design and maintenance problems, including thin concrete, inadequate reinforcing steel and weaknesses in the foundation, a panel of engineering experts reported Wednesday. A forensic investigation team said it was issuing a preliminary list of causes so that engineers do not repeat the problems as they rush to fix the spillway before the next cycle of rains begins in November. The two-page report does not identify what initiated the failure along the 3,000-foot chute that was used to drain the reservoir during massive winter storms.