Mont. Code Ann. § 26-1-706

After entry of a judgment in an action for damages, any voluntary partial payment made up to that time must be treated as a credit against the judgment and must be deductible from the amount of the judgment. If after partial voluntary payments are made as provided in this section, it must be determined by a court of competent jurisdiction that the person who made the payments or on whose behalf the payments are made is liable for an amount that is less than the amount of the voluntary payments already made, the person may not have a right of action for the recovery of the amount by which the voluntary payments exceeded the amount of the judgment.