(a) Except where the motor vehicle has been seized as described in paragraph (6) of subdivision (b) of Section 2983.3, any provision in any conditional sale contract for the sale of a motor vehicle to the contrary notwithstanding, at least 15 days' written notice of intent to dispose of a repossessed or surrendered motor vehicle shall be given to all persons liable on the contract. The notice shall be personally served or shall be sent by certified mail, return receipt requested, or first-class mail