Can you explain this in more detail, please? Are the seats just dirty or is the side of the bolster worn to the point that the color is missing? If so, no "cleaner" in the world will fix that.

That said, you may be experiencing some of the downside of owning such light colored leather upholstery. It's easy to get overly aggressive when cleaning leather, whether with a cleaner in a bottle or with steam. Steam works wonders, by the way, but you do need to use common sense with it so as not to damage the coating over the leather itself.

If the seats are just dirty (and from the sounds of it they're quite dirty) then it's no big shock that our basic one step leather cleaner didn't bring them back to like new condition. It's a very light duty cleaner with excellent conditioning properties, and if used regularly from the get go it does an excellent of preventing dirt build up. But most people, like the previous owner of this car it would seem, can't be bothered with routine maintenance. Of course, they then become really annoyed when they can't clean things up after letting them go for too long. Or in your case, you simply become annoyed that the previous owner was a slacker.

If you have a Costco membership then their house brand all purpose cleaner might be a good choice. It can be diluted with water and should be perfectly safe on the leather. Meguiar's All Purpose Cleaner is a heavily concentrated cleaner from our Detailer Line but it's not generally found in your typical retail outlets - you would need to seek out a specialty detailer supply shop for it. But even diluted as far as 10:1 with water it's has been shown to safely remove some pretty heavy soiling from automotive leather. Smallest size available is one gallon, though.

A small home steamer may be your best bet in the long run. Use either a terry cloth towel with it, or a soft boars hair brush, and take your time with it. Just use common sense and don't overheat the leather or dwell in one area for a long time. Obviously you'll need to apply a leather conditioner after this, but you should be doing that on a regular basis anyway. As should have the previous owner.