stainless lines actually present their own issues, being more cathodic, they'll eat aluminium and steel fitting alike. I'm not so worried about sulfur, mostly would be dealing with sodium chloride(as road salt), copper-nickle shows superior corrosion resistance in 'salt sprays' over everything...
what I'm doing. I'm trying to install copper-nickle brake lines but I'm trying to figure out what fitting to use. options are brass, steel, or stainless(which would fluctuate between active and passive given road salts, etc). I'm joining with aluminium and carbon steel and obviously...