Mont. Code Ann. § 70-23-610

When the purchaser of a unit obtains title to the unit as a result of foreclosure of the first mortgage or trust indenture, the purchaser and the purchaser's successors and assigns are not liable for any of the common expenses chargeable to the unit that became due prior to the acquisition of title to the unit by the purchaser. The unpaid share of common expenses is a common expense of all the unit owners, including the purchaser and the purchaser's successors and assigns.