The amount recovered under section 3031 shall be applied first to the payment of the costs of the civil action and officer's fees on the execution and next to the payment of the amount due on the mortgage. The balance, if any, shall be retained by the insurer and paid to the mortgagor. If the insurer assumes the defense, it shall be liable to the plaintiff for costs in the same manner as the principal defendant, defending the action, would be.   [PL 1969, c. 132, §1 (NEW).]