If this shotgun has the extension rib with the "window" in it, it is a good chance that the slope is worn causing the lever to the left. Most that have this type, will use the rotary bolt, that has it's own slope built in to it, and very seldom does this wear compared to the extention rib with the window.
Unless you shoot this gun a few times a week and shoot hundreds of shells, you will probably never wear this out as this was what it was made for.

David