I would suggest trying OPC again. The label directs you to use 3:1 for most cleaning jobs and less diluted or even straight for tough cleaning. According to your post you used it at almost double the dilution that we recommend. I admit I make my own dilutions for specific cleaning, but I would recommend following the directions before I stopped trying power clean or bought another product. Also, the SV brush is not the best choice for cleaning leather. A short bristled horsehair or soft nylon nail brush would be a better choice. Finally, if the stain is dirt/sweat/grime OPC will remove it, however, if it is dye transfer from clothing it may have penetrated the panel and is there to stay. If that is the case you'd need a ready to restore the color.