Yeah I'll go with a sharpie. The finish seems to be more original with it in my opinion. Of course the ideal situation is to take it to the dealership but than you have to pay for it. If it's minor, stick with the sharpie.I used a sharpie on mine and it's not noticeable at all. I did it about six months ago and it hasn't faded.
My radio dial also had a crack in, so I ended up going to the wreckers to get a new one. I called my local GM dealer and they wanted like $30 or $40 for it, so be prepared for exorbitant dealership prices.