I bought a second hand van - a 2001 Movano - from a car dealer. He noted that there was oil leakage on the receipt. I had a mechanic go over it and he made various repairs, including a new cambelt and brake pads, before I drove it to France. It worked fine. On my way back to Calais, the van started making juddering noises and failed to accelerate. I got it off the motorway and it was recovered to a garage by the AA. They say it needs a new engine. What are my rights?