Try this first put the whole unit in the freezer (a chest freezer is colder than the one in your fridge) and leave it there for a while over night or a few hors at least. Then get your tap water as hot as you can and gently heat the area just below the fitting and wrench it. If you have a vice use it ( I try to place a couple of small pieces of wood on each side to keep from scratching, also try to have this set up before you do the heating part) them wrench off the fitting. Aluminum expands quite nicely when heated even by water.
Did you try to tighten it a smidge to try and break the seal? Some times the smallest movement is enough to get her moving when you take it off. I'd avoid using a torch for now untill you try the hot water first, I'd hate to see the anno get messed up. You can also try to use a red magic marker to cover the scuff if it's bothering you.
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