My 06 GS300 has tan leather seats. On the drivers side, the lower (lumbar section) back of the seat has a sort of dark section, almost looks like the seats were black and dyed tan (obviously that's not the case) and the tan wore off a bit from getting in and out of the seat. The car only has 16k on it, so I doubt it's wear. More like the dark blue or black from the previous owners pants has left a bluish/black area.

I've scrubbed with Lexol leather cleaner to no avail. Any suggestions?

 

This is likely from bluejeans. The dye in jeans is not fixed and will cause issues for light colored leather.

I've worked on a couple of cars with this issue. Here is what I've found. Tell the owner to wash his jeans in salt water. This will fix the color and minimize the future transfer of color.

I have had good results removing these stains with the Lexus branded cleaner. I've also had good results with Meguiar's #3916 Heavy Duty Vinyl Cleaner and D18001 Leather Cleaner and Conditioner from their Detailers line. Use a brush and agitate the area into a foam and then let it set for about 5 minutes but do not let it dry. Wipe with a a clean towel and let it dry. Reapply if needed.

The leather is coated with a vinyl-like urethane coating so you need to be pretty careful using abrasives but some people have had success with a Magic Eraser. If you overdo this you will ruin your leather so if you decide to go that route be aware of that fact.

What has happened here demonstrates that the coating applied to the leathers is indeed porous. Sweat leached through the jeans carrying the blue dye into the leather. For those who think that the leather conditioners will not penetrate and will absorb conditioners, take note.

 

If you start to see tan color on the towel..you will know you've gone through the clear coat. Make sure at all costs not to do that.
It seems like this is permanent staining though, but at 16,000 miles, it shouldn't be the case.