Originally Posted by
flyingmusicianlax
AS arrives in Terminal 6. From there, you'll want to collect your luggage (if any) and catch the interterminal shuttle (which is landside).
OP will not check luggage, but if OP would, AS and AA have an interline agreement so OP should be able to check in luggage in SEA all the way through to Buenos Aires.
I have no experience with the LAX Flagship lounge, but in ORD it is less than spectacular. The self pouring alcohol is nice, but the premium bar in the Admiral's Club is better and you get (a) drink voucher(s) - much depends on the lounge AAgent and the quality of your friendly smile.