You can buy at the big box store replacement door jambs. I cut and fitted a replacement piece. I have a router bit to cut a slot the thickness of a biscuit. I cleaned the area well and put a bed of caulking in. Then secured the replacement piece with the biscuit, shims, gorilla glue and brads. The brick molding was put on and it covered the slot for the biscuit and gives strength to the repair.