Assessment of common expenses. Liens and foreclosure.

(b) Where a mortgagee or a purchaser at a foreclosure sale obtains title to a unit, such acquirer of title, his heirs, successors and assigns, shall not be liable for the entire unpaid share of the common expenses or assessments by the association of unit owners chargeable to such unit which became due prior to the acquisition of title to such unit by such acquirer, but such expenses or assessments, if not fully satisfied out of the proceeds of such sale, shall become common expenses collectible from all of the unit owners, including such acquirer, his heirs, successors and assigns.