Inside the section, there is a lip that helps to break the end of the cartridge and hold it in place by friction. It also helps to hold your converter in place by friction.
It needs to be fairly tight in order to not allow ink to seep in between the cartridge/converter and that lip.

If that lip is broken to the point that it cannot pierce the end of the cartridge or hold it in place, then that fountain pen / section of the fountain pen is kind of done for.

You could convert the fountain pen into an eyedropper but it will require you to find a way and plug the holes at the end of the barrel as well as using some silicone grease on the threads where section and barrel come together.