BERLIN/WASHINGTON (Reuters) – Volkswagen is struggling to agree with U.S. authorities a fix for vehicles capable of cheating emissions tests, a VW source said on Tuesday, showing how relations between the two sides remain strained four months after the cheating came to light. The source said the German carmaker would hold further talks with the Californian Air Resources Board this week and with the U.S. Environmental Protection Authority (EPA) next week, and still hoped to reach a solution by a mid-January deadline.