Go to Orchard Supply or some hardware store. In the Industrial section, u can buy a 9/16 ( take it to the car and check for a fit)allen wrench for about $5.00.

Then get a persuasion bar ( piece of metal pipe anout 1.5 - 2 ft long). Spray some WD40 or some other rust eater and let it sit for sometime.

Plug in the allen wrench and put the other end into the persuasion bar. That should do the trick.

No need for overkill!