Take it out again and carefully straighten the tangs that clip into the holes in the front section. These are easily bent back. Be gentle. It is a bit awkward. If its bent a tab back it wont go in Take it slow and they will eventally go in. It took me several attempts. Dont bend or break the tangs or you will be in trouble. Mine went back really easily... on about the 10th try. Then fix the fixing nut back. Dont miss the metal sleevelet out. I could not see why it was so difficult. BE GENTLE.