The longest oil filter cover bolt broke off deep in the hole while I was tightening it back up. It broke far before it was tight at all. After looking at it, I think it was defective metal. I want to pass along my fix in case it may helpful to someone else. I first decided to drill a small hole in the center of the bolt end (that was deep inside the bolt hole). I was planning to use an easy-out to extract the bolt. I thought a small bit would be choice to keep from getting into the side of the hole or threads. The small bit was able to flex and thus veer off in the wrong direction. This didn't work. After about 6 hours of other attempts at various techniques, I was finally able to get the bolt out. I took a piece of 1/4 inch copper tubing and placed it into the hole to act as a sleeve to keep my bit straight. Then I bought a reverse drill bit that would just fit inside the copper tubing. You can purchase reverse drill bits at some Ace hardware stores and other tool specialty stores. With the sleeve in the hole and a bit big enough to be rigid, I was able to keep everthing very straight. I oiled the bolt good and reverse drilled the broken bolt. Once the drill bit got a bite on the broken bolt piece, it just spun it right out. I was never so excited in all my life after working so hard to get that bolt out. I just want to pass this along in case someone else can use some ideas with a similar problem.