A health service corporation writing hospital service contracts or medical service contracts may not commence business and enter into any contracts with subscribers, nor secure any application therefor, unless the corporation has a contributed surplus of not less than one hundred thousand dollars. A health service corporation writing health service contracts other than hospital service or medical service contracts may not enter into any contracts with any subscribers, nor secure any application therefor, unless the corporation has a contributed surplus of not less than twenty-five thousand dollars. The contributed surplus is repayable when the unassigned earned surplus exceeds the amount required to be initially paid in as contributed surplus, only if the payment does not impair the working capital of the health service corporation.