How do you know a valve is sticking?Changing a head gasket isn't that bad, if you have done work like this before. Is this a 4 banger or V6? The four will be much easier.This would be a good time to change the timing belt and the water pump, if it's got a lot of miles on it. Some people have success using seafoam in their engines. I am living in Germany so I don't know that much about the stuff.