At the time of the initial sale of the unit and upon each successive price-restricted sale, the initial purchaser shall execute and deliver to the Administrative Agent a recapture note obliging the purchaser, as well as the purchaser's heirs, successors, and assigns, to repay, upon the first non-exempt sale after the unit's release from the restrictions set forth in this section, an amount equal to the difference between the unit's nonrestricted fair market value and its restricted price, and the recapture note shall be secured by a recapture lien evidenced by a duly recorded mortgage on the unit.