Another trick to get seized fittings apart is the dual-wrench trick. Of course, we all know about using a wrench to hold one side steady while turning the other side. In this case, the key is to turn the side you want to remove back and forth a little at a time. A 64th of a rotation is all you should expect here, and you will eventually end up with a little pile of oxidized aluminum that will fall out of the fitting. Back-and-forth, back-and-forth, repeat a few hundred times, add lubricant if it is really tight, and it will usually come apart with enough good thread left to reuse-if you were patient enough.