i just broke mine off too from scraping snow off, if the stud is broken off from the base you need to get a new one. at the dealership i think i just paid $7 for mine. i'll give crispy credit for this cause he told me how to do it the other day:
take out your dome light, there's a foam peice stuck right inside the roof (easy to see), pull that out and you have a star bit holding the antenna wire to the base of the antenna. just loosen the screw, the broken one pops off and the new one goes on. it took me less than 10 minutes to do a swap.