I'm pretty sure it's sun screen. When I turn around to back up, my arm hits that part of the seat. And also the back of my legs on the other part of the seat. Last summer, I probably put it on before going out and it accumulated over the summer/fall (that's when I noticed it). I am going to try some leather cleaners other than Woolite. That didn't work at all. Leather Masters has to be shipped. I may see about some other options. Appreciate your help.
Thanks,
Peg