1. Don't use stones on aluminum. Use carbide burrs.
2. A Dremel will take forever and I doubt that you can reach in far enough with any bit that will fit in a dremel. Borrow or buy a die grinder that accepts 1/4" shank bits. Either pneumatic or electric. You can get a cheap one at Harbor Frieght that will work.
3. Several posts have already mentioned what to use on the bits to keep them from loading up with aluminum. Pick one. They all help.
4. Don't use stones on aluminum.
5. Whoever you talked to at 440source is an idiot for suggesting that you could fix this with a dremel.
6. Did I mention, Don't use stones on aluminum.