My daughter has a 18 ZL1. The old man was cleaning the interior (it had been 6 months) and noticed how crappy the steering wheel looked. I tried a bit of soap and water and a Adams interior brush. It cleaned some of the wheel but in the thumb notches its was still very dirty. What chemical should I try to clean the stubborn spots on the wheel. The rest of the microfiber interior just needed a good brushing and vacuum attention.