Section 315. Claim for deficiency after default and repossession

If a buyer
  defaults on any instalment of the time sale price and the holder obtains
  possession  of  the  motor  vehicle  and  disposes  of it as provided by
  section 9--610 of the uniform commercial code, the buyer shall be liable
  to the holder for any deficiency to the extent provided in that section;
  provided, however, that in calculating such deficiency  there  shall  be
  deducted  from  the amount thereof as prescribed by such section 9--610,
  an amount equal to that portion of the refund credit to which the  buyer
  would  have  been  entitled  under  section  three  hundred five of this
  chapter if, at the time the holder disposed of the  motor  vehicle,  the
  buyer had not been in default and had prepaid in full the balance of the
  time sale price as the amount realized upon the disposition of the motor
  vehicle bears to the balance of the time sale price.