The provisions of this act shall not affect any act done, liability incurred, or right accrued or vested, or affect any suit or prosecution pending to enforce any right or penalty or punish any offense under the authority of any Act of Assembly, or part thereof, repealed by this act: Provided, however, That in any case final on or before June 12, 1972 in which a defendant was sentenced for the commission of acts similar to those proscribed by subsection (16) or (31), but not (30), of section 13(a) of this act, such defendant shall be resentenced under this act upon his petition if the penalties hereunder are less than those under prior law and in such case the prior criminal record of the defendant shall be expunged to the extent that such record shall no longer contain any reference to the prior grade of the offense if higher than the grade of the offense to which defendant is resentenced.