When any piece of a helmet buckle breaks off, you must replace the buckle! Some manufacturers will send you a replacement buckle if you simply contact them. Otherwise, try your local bike shops for replacement parts.
After time the fit pad anchors attached to the inside of your helmet may come loose or fall off. Some manufacturers recommend 3M Super 77 adhesive to reattach the anchor.
Plastic Shell Separates From EPS Foam:
You can use the same 3M Super 77 to reattach the plastic shell to the EPS foam of the helmet.
If your strap stitching comes out contact the manufacturer about a repair or to order a new strap. If they can't repair or replace the strap, purchase a new helmet.
Repairing Damaged Foam:
There is no repair to the foam Core. If damage has occurred destroy the old helmet (so no one can use it) and purchase a new one.