Section 422. Claim for deficiency after default and repossession

If a buyer
  defaults  on  any  instalment  of  the  time  sale  price under a retail
  instalment contract, and the holder  obtains  possession  of  the  goods
  which are the subject matter of such contract and disposes of such goods
  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  four  hundred
  eight of this chapter if, at the time the holder disposed of such goods,
  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
  goods bears to the balance of the time sale price.