Or if you have a plumbers torch and map gas or larger set up. Get that nut good and hot, it'll expand enough you should be able to free it up if penetrating oil isn't working.
This, but also please, please, don't use a cheater on it. It's a PITA to fix those bent swivel handles. Soak it in some penetrating oil of your choice and have a go at it afterwards. Shouldn't take much to get it free. Go easy on the lock handle though, you'll hate yourself later if you pretzel it up.
I cleaned it up a bit and managed to move the handle about 1/5 of a turn! (still stuck though) - and in the process of moving the handle I mostly bent it back into shape...