there is an excellent product called leatherique you can get from www.emmonscoachworks.com Its a 2 part process which you put on and leave for a few hours which will take all the dirt and salts from sweat that have soaked into the leather. The other take off the stuff which works excellent on plasic doors too. I am an airplane mechanic so i'm always dirty and i used this stuff and my seats and steering wheel came out like new. I was so impressed im thinking of opening one of these stores!! Its comes as a kit for $35 My seats look and feel like new. Its an awesome product. Many ferrari owners use it. Zymol also has a very good product but its more pricy and i like the leaterique products much better!

Good luck!