Another vote for the mid sized socket. On mine the shallow socket wouldn't allow enough for bolt clearance and the deep socket hit the fenderwell.
Hit it with a propane torch until it's just about red hot, then spray it with some WD40 or PB Blaster. The hot nut versus the cold penetrating oil will draw the oil into the threads. Be warned, it's going to smell like a BBQ grill under the car and smoke a lot, but it works very well in getting stubborn nuts and bolts free.
Just heat it up with a torch and it should come right off. But make sure as soon as you get the torch off of it, go ahead and try to get it off. it should come right off. Or if you dont have access to a torch take it to a muffler shop and get them to get it loose for you and then swap it out yourself.
Use one GOOD swivel and put some elbow grease into it. I broke two swivels trying to remove mine before I got a higher quality swivel that was able handle all the force.