I've seen quit a few leakers on head bolts and always use a sealer. I use the locktite 242 if I remember the number right. I have seen other types out there but can't recall the name. I personally don't like taking a chance on leaking water into my oil from the headbolts that do penatrate into the water jacket. I also know quit a few folks that have never used any sealant, some end up with leaks while others have never leaked?