Any funds accepted by a member association or association MLS as deposits for lock box keys shall be retained by the association or its MLS in a separate account so that the funds will be available to be refunded to depositors upon return of the lock box key to the association or its MLS. The funds deposited are to be retained for this purpose only and are not to be utilized in any other manner. The separate fund may be an interest bearing account with the interest retained by the association or association MLS unless as a requirement of law, or at the discretion of the association or association MLS, such interest shall be paid to the depositors. M