Every mustang w/ leather has that same problem and it only gets worse. I test drove 2 01 cobras in the summer that had that problem so bad that it made the car look cheap. That stuff looks nice new but that's about it.
mcgwyer's (dont know how to spell it) makes a leather conditioning oil...but once its rinkled, its too late.....its a preventative maitenence thing. my 99 expedition has leather seats, i apply that stuff about once a month.
I got those wrinkles in my car too.:cuss: There's no way of preventing it. I'm pretty anal so I will be having the seat redone about every 20k miles. It's crazy isn't it?
It's a cow's ass.:shrug:
It's not just a Mustang thing. Any car w/ leather will do this, eventually.
The best you can do is keep them clean and conditioned.
I had a '94 Callaway Camaro with Callaway leather seats. Cost me $2600.00 installed. The exact same thing happened with the drivers seat (which got the most use of course). It's something you live with if you have ANY leather seat IMO. I used leather conditioner regularly but it never helped. They must have used an old cow! LOL!
My C43's leather seats never cracked or got significantly wrinkled in four years of owning it, with 52K on the clock. I used leather conditioner once a month, but I also think it is the type of leather too. Avoiding UV rays on the leather makes a huge difference too.