Soak it, yes. For a few hours. There's an O-ring securing the cap to the body, you might have to replace that once you get it unstuck, sometimes the baccy juice eats it ..... a proper-sized one from the plumbing section will do.
Remember, a stuck cap is better than a loose cap. As long as the draft hole in the cap is aligned with the same in the bottom of the bowl, you should be fine.