For prohibited transaction penalty proceedings, this section shall
apply in lieu of Sec. 18.5(b) of this title. Failure of the respondent
to file an answer within the 30 day time period provided in Sec. 18.5 of
this title shall be deemed to constitute a waiver of his right to appear
and contest the allegations of the notice, and such failure shall be
deemed to be an admission of the facts as alleged in the notice for
purposes of the prohibited transaction penalty proceeding. Such notice
shall then become the final order of the Secretary, except that the
administrative law judge may set aside a default entered under this
provision where there is proof of defective notice.