The nose of the solenoid, where the orifice and seat are, has an O-ring. This ring can stick in the manifold. The rear of the solenoid, where the needle and electrics are, threaded to the nose and to the manifold.
When you unscrew the solenoid from the manifold and the O-ring on the nose sticks, you end up unscrewing the nose from the body of the solenoid.
When this happens, you need to push the solenoid back into the manifold and give it a couple of turns. You want it to catch the threads on the nose piece without threading into the manifold.
Once you manage to do that, pry the solenoid away from the manifold. It should pop out with the nose piece. I've done this, it works.
2003 Alpine Coach 40MDTS - 400HP Cummins ISL
Can Am Spyder Roadster