The German government is studying a proposal from Opel and its parent company, General Motors, to save the struggling carmaker with a huge cash injection and a cost-cutting plan. The proposal calls for GM to sell off a stake in its Opel unit, the core of its European operations, in order to win $4.18 billion (€3.3 billion) in government support from Germany and others in the region, said Andreas Kroemer, a spokesman for GM Europe.