This is a very common flaw. The C-shaped piece of spring wire that anchors the lever often exerts considerable outward pressure. It may be enough to cause gradual cold creep in the barrel material over a period of decades, though more often the gapping around the lever requires the barrel to be exposed to enough heat to soften its material.
To fix it, you'll first have to take out that lever retaining spring, then use heat to restore the original shape of the material around the lever opening. Very easy to do irreversible damage, though.