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 non-restricted 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.