I have not taken that bolt off yet so I'm not sure what size it is. It looks like you could remove the sprocket that way but I have not tried it.

Here is pictures of that part in the manual. Do you have a manual? If not I think there is a free PDF of it you can download out there somewhere.

I can post pictures of any step in the manual you need, just let me know.<br type="_moz" />

Try a titanium or diamond tip bit. Use a tiny one for a pilot hole. Once you have a pilot hole you should be able to drill succesively large holes until you can get in an easy-out. The vibration and heat generatedduring this process will help loosen the locktite. But even still add more heat.

This is expensive an time consuming but consider what it would cost to replace the entire unit.

HSS are garbage for any but wood. A good cobalt or carbide bit would work, carbide is more brittle if trying to drill by hand.