What does everyone use to clean leather seats that need cleaned badly? Or if someone knows of something pros use. Thanks in advance Merry Christmas!

Over the weekend i had the boat at the lake and came out sunday morning and noticed right by the fuel filler on the hull i am guessing some fuel sloshed out and got on the hull. Well now i have a nice little stain there are there any tricks to getting this out? If not what has to be done to...