The Perils of car buying, Part 2

I received the £172 refund from the AA, but they are still adamant that they will not pay the extra £68 to compensate for the extra cost of rectifying the door lock. I then write to the previous owner to ask whether the door locked correctly prior to its sale. Unfortunately for me, it did. So, rather than taking this issue further through the Small Claims Court, I will just let the matter ride.