A valve that sticks tight enough to cause the rocker shaft to break doesn't need any halfway measures. I'm all for doing this type of work once, and getting it right, not doing something halfway and trusting to luck. A couple of hours of labor time and a head gasket isn't all that expensive, and the problem can be assessed much more accurately. A healthy dose of KROIL might solve the problem without pulling the head, but I'd be spooky about the possibility of more trouble unless I got a look at the inside of the valve guide and the condition of the valve stem.
Jerry
