Ruddockus

Evening all, We recently sold a VW Scirocco auto to a punter in Jan 2017, he's contacted us to say the gearbox was playing up in May 2017. We have an AA report to show no issues with the car at date of purchase and he has a WMS Group 4* warranty. He called the warranty company and said he was having problems and they advised him to tow the car to their recommended repairer, to save himself the recovery cost he decided to drive it there! Once at the garage they wanted to know who was paying for the diagnostic diagnosis and any other investagative works that they would need to be done, he did not contact us or the warranty company instead chose to remove the car and drive it around somemore until the gearbox is now completely knackered and he has his own garage now wanting £4200 to repair. When we first were in contact with him we asked if the car was like this when he first got it and he said no it started 3 months later which we have in text message format, also we have the AA report. Is this grounds enough for us to reject his consumer rights issue demanding that we rectify these issues? The warranty company have all the things that have happened documented including him ignoring their advice and to continue to drive the car. If we end up in court what are the chances of us winning? Thanks in advance