I called the Kitchenaid Customer Service line today to register my product as well as ask about the gray streaks. Of course the first advice the agent had given me was to never wash the bowl or the beater in the dishwasher (which I hadn't) and when washing by hand to dry both right away.
Second, when putting the bowl onto the holders you need to check and make sure the bowl is completely level. If it is not level, you need to push really hard until you hear it click into place. This was one of my mistakes ... I thought the bowl was on tight enough but it wasn't so my bowl was always tilted a little bit.
Third, she had me test whether my beater was at the correct level. She had me get a dime and a flat head screwdriver. With the bowl and beater in place, she had me put the dime into the bowl. When the beater is turned onto the "Stir" setting, the beater should be moving the dime 1/4 inch per rotation. If it is not touching the dime, the beater needs to be adjusted. With the flat head screwdriver, she had me turn the screw that is just to the left of the mix handle 1/4 turn counter clockwise and retest. I had to do this twice before it was correct.
Now my mixer is running perfectly. And as a positive, they are sending me out a replacement mixing bowl and beater. Both received a small amount of scratching due to the beater not being adjusted properly. She did let me know that all of the materials are food safe, so the scratching would not harm any of the food I have made.
I just thought I would pass this info along to others as it was very useful to me!!