Replacing my valve guide seals on a 94 Mazda b3000. Got a rocker arm bolt that refuses to come off. I've been using a 10mm and had no issues but this one is going to require alot of torque to take off. I'd like to make sure I don't strip it or twist the head off of it. I'm using 6 point sockets only. Not real sure what to do. Wanna make sure I have the exact size for one thing.