(a) If at anytime the assets of a domestic mutual insurer doing business on the cash premium plan are less than its liabilities and the minimum surplus, if any, required of it by this title as prerequisite for continuance of its certificate of authority, and the deficiency is not cured from other sources, its directors may, if approved by the Commissioner, make an assessment only on its members who at any time within the 12 months immediately preceding the date such assessment was authorized by its directors held policies providing for contingent liability.
(b) Such an assessment shall be for such an amount of money as is required, in the opinion of the Commissioner, to render the insurer fully solvent, but not to result in surplus in excess of 5 percent of the insurer's liabilities as of the date of the assessment.
(c) A member's proportionate part of any such assessment shall be computed by applying to the premium earned, during the period since the deficiency first appeared, on his contingently liable policy or policies the ratio of the total assessment to the total premium earned during such period on all contingently liable policies which are subject to the assessment.
(d) No member shall have an offset against any assessment for which he is liable on account of any claim for unearned premium or losses payable.