You must crack the seal and it's a scary thing to do but you will definitely do it with more care than a garage would .
Ideally you will find a piece of metal that will sit flush on the barrel all around to spread the impact evenly and avoid damage (an old barrel maybe) . Then against everything you have ever been taught about mechanics whack it as hard as you can with a metal hammer , the harder you hit it the more likely it is that you will break the corrosive seal between the barrels and the casing thus avoiding having to do it again . Once the barrel moves just tap it lightly out .
Mechanics is a precision trade but when precision fails brute force is often the way forward .