What you are seeing is the leather dye failing. The leather "dye" on the wheel is really more like flexible paint. It is failing from all the sun exposure on the top of the wheel. You can refinish it yourself. The process is to remove the wheel, sand smooth with fine grain sandpaper, clean, redye, and then clear coat. I know the Leatherique people sold kits to do this, and so did some other vendors. Google is your friend here.