Have you tried putting back pressure on the bolt?
In other words, get a small vise grip (in lessor cases you can use your finger - always a good place to start) or finger and place it on the reverse side on the head and push as you try to screw it out. I KNOW it sounds like I am describing something else, but stay with me here….
It is only Aluminum so even if you have to get mean with that bolt you should still be able to get it out! You may have to re-thread to a larger size, or replace the bracket but you should be able to "un-stick" by using a little reverse wrench-ology.
Good Luck and may all your bolts work free…goodness knows no one else is working or free in the US now (a little political humor there for election season).
