thanks well now i have a problem,

I used a tool to remove the "special nut", it broke free with a little force, and then broke away from the base. My problem is that the head of the "special nut" separated from the threaded base. The base is still in the antenna unit. Im sure it hasent been removed sence the day the car was built. I think the threaded part corroded and fused to the area around it.Any ideas on how to get it out? I really dont want to have to buy a whole new antenna unit, as i dont need one, and they are expensive.

thanks