I concurr about the rejuvinator oil and prestine clean. However, let me offer one less-expensive, more readily available suggestion (albeit a little unorthodox):
I've had good luck softening leather seats with Neatsfoot Oil and/or Baby Oil. When I first heard of this method, I was quite skeptical and thought it would likely do damage to the seats. I've tried it since that time on a few different vehicles and have seen NO ill effects WHATSOEVER from it. What I would recommend is that if you want to use both, clean the leather as thoroughly as possible with your woolite mixture and a nail brush, and let it dry completely. Once dry, apply a liberal amount of baby oil to the seats, and let it soak in for a couple hours (if you're lucky, in direct sun so the interior gets hot and helps the leather wick up the oil.) After that, come back and wipe off the excess oil. Let it sit for another hour or so, then come back and repeat the process with the neatsfoot oil. An added bonus of the neatsfoot is that it acts as a water-resistant sealer. After you've wiped the excess oil off and let it sit again, you can re-clean the seats with woolite or another "proper" cleaner (do it lightly though!) and dress/condition it with the PB product you already tried on them.
I know it sounds odd, but I actually got these tips from the shoe repair world; I was talking to them one day about how to clean and re-condition some older dress shoes I had, and this is what they suggested. So, I applied the same principle to automotive leather and found out that it really DOES work!
Good luck with which-ever way you decide to go.
