Quote Originally Posted by coupe3w View Post
I would heat the manifold around the bottom of the plug with a small propane torch and then try and loosen it. Just make darn sure you have no gas fumes around.
Sometimes you can heat the manifold as suggested and smush a candle around the threads. The tallow will run into the threads and allow a little lubricant into the recesses and make it easier to turn out with a socket and long bar. Also, sometimes, giving it a slight turn tighter will break it loose.