[Jdub]

A classic issue. I suggest you heat it up first, MAPP or Acet, as well as you can esp. if it is a through bolt (both ends), then take a punch and hammer and tap it sharply, This serves to break some parts of the corrosion. With the bolt still warm, douse with penetrating oil (I like Acetone and ATF), and tap a few more times. Heat it up later just for fun

Now get a good quality new drill bit and quality easy out kit and have at it. The overall philosophy here is to loosen the item as much as you can before applying the final solution. Heat is always your friend and perversely it seems applying a tightening torque to snapped bolts helps. I assume it just lets the penetrating oil get into more surface area.

Good luck you will pull this thing out.