[bacampbe]

I've got an M235i convertible with red leather. I drive top down most of the time. I noticed yesterday that I am getting an accumulation of black grime on the back seats. It's sooty and sticky; it reminds me of brake dust or the carbon accumulation you see around tail pipes. (I'm now a bit worried about exhaust blowing into the passenger area when top-down, but that's a different concern.)

I went after it with Maguires Gold Class leather cleaner. That took most of it off, but there are still a few shadowed looking spots. Are there better choices to completely remove this?

[Lucky13]

This is why I always kept my back seats folded down in my 2007 335 convertible. I actually keep my back seats folded down in my M235 coupe to keep the leather clean and keep the sun from fading them. Getting back to your question the best thing I found for cleaning really dirty, stained leather is using a stain eraser foam pad (mr Clean may make them) but Turtle wax makes a Luxe Leather you put on this applicator and it cleans bad dirty spots. I used this on a 2000 528 with beige seats that were dirty and stained and it did a really good job. I can't remember if the eraser came with the Luxe Leather but any retailer with household cleaning products sell the foam erasers. I typically also use the same Meguires as you to maintain the seats.
I just went on line and looked it up but the Luxe Leather Kit comes with two of the pads in the kit, when I cleaned the old 528 I had to buy the Mr Clean Magic Eraser pads separately to finish the project because the seats were so dirty and stained. You just apply the Leather cleaner to the pads and go for it.