the three month thing is relative as well. if you bought a £500 run about and the engine went in two months, then you could say the rest of the vehicle is worth the value and that is the risk. car prices would never drop below traders prices otherwise.

in all seriousness, i'd see a solicitor, simple letter will have them getting it all sorted. get it all down on paper in regards to time scales and any factual information. do not conjecture if not substantiated beyond doubt. easy for a forum to tell someone that they'd do something one way and you should do the same, not all people can handle situations the same way to their advantage.