If Toyota do agree to fix it under warranty, try to get them to replace the entire squab cover instead of just repairing your existing cover. Also, for the record, the damaged seam pictured is called a 'french seam'. This type of seam has no piping sewn into it and can be a bit of a bugger to repair properly if the leather is worn right through (as opposed to just scuffed).
Thanks Guys,
Yes it is the "French seam" and you are correct, there is no piping. It's only a small crack, but it looks as tho' it goes right through. I have only had the car since it was twelve months old. I don't know how it was treated before I got it. I make sure I get in and out without scraping across the swab. I've been using mothers leather on it and its not got worse, but it bugs me as the car is otherwise pristine.
Thanks for the comments.
Tom