Whenever the lawful invested assets of any mutual life insurance company shall exceed the reserve and other liabilities to an amount equal to the amount of the guarantee capital subscribed, the directors or trustees, at their option, may retire or return all or such portion of the guarantee capital to the subscribers as the interest of the company may warrant; but no sum in cash shall be returned exceeding that actually paid in, with the interest due and unpaid.
40 P.S. § 613