Oh, be very, very careful about using even a mildly abrasive sponge or cleaner on GE's aluminum. My husband cleaned the front of our Advantium with a 'safe' scrubby, only a month or two after we got it (back when they were going for about $1200), and left it horribly scratched--something I've had to live with for the past 12 years!

Have you tried using a baking soda paste on it? Let it sit for a bit, and wipe with a soft cloth--baking soda is non-abrasive, and usually does the job for me, for so many different cleaning tasks, that it's the first cleaning product I reach for.

I just use Easy Off oven cleaner (no fume in the blue can). Spray it on and give it a few hours and that stuff wipes right off with a sponge.