So I not the only that found the easy outs got a tendency to break off. The reason is the head bolt and other steels bolts can be galled to the aluminum and become as one piece.
Okay here a tip if you plan to try drilling the broken portion. First using a center punch make an indention dead center of the bolt to drilled out. Now don't try drilling completely in one step; instead, use step drilling process. This involves using a fairly small sharp split point bit at first as to not drift off center and drill as straight as you can through the bolt. Then using gradually increasing sizes of bits work your way out drilling. Once you reach the tapping size you want stop and tap. Hopefully you have enough area around the through hole in head as to allow you to enlarge it if you need to oversize to the next bolt size as some taps can't cut the head steel without breaking.
Just last week I had to drill out a steel bolt in a Kohler head to accept a new bolt so I could bolt down the valve cover. I manage to go from 6mm to 7mm so I was lucky.
