There are seals because it is important that the plate is tight on the inside of the basket but this can happen if you try to insert the plates dry.
Try dipping them into water or spraying with sanitiser before inserting. When you are filling grain into the basket it gets dusty on the sides – this grain dust will also help the plates to slide down easily without the seals coming off. You could even sprinkle grain dust on the seal before inserting.
It is also a good idea to ease them in on an angle and then straighten up to make it easier.