Mont. Code § 35-15-403
An assignment of stock may not be made to any person who already owns stock, except by the consent of the board of directors, but stock may be assigned to the association at any time with the consent of the directors. On a question a stockholder may not have more than one vote. Every assignment of stock on which there remains any portion unpaid must be recorded in the books of the association, and each stockholder is jointly and severally liable with the association for the debts of the association to the extent of the amount that is unpaid upon the share held by the stockholder. An assignor may not be released from the indebtedness by reason of any assignment of the assignor's share but remains jointly liable with the assignee.
§ 35-15-403, MCA