Failure of a respondent to file and serve an answer within the time and in the manner prescribed by Sec. 302.408 shall be deemed to authorize the DOT decisionmaker or administrative law judge, as a matter of discretion, to find the facts alleged in the complaint incorporated in or accompanying the notice instituting a formal enforcement proceeding to be true and to enter such orders as may be appropriate without notice or hearing, or, as a matter of discretion, to proceed to take proof, without notice, of the allegations or charges set forth in the complaint or order; Provided, that the DOT decisionmaker or administrative law judge may permit late filing of an answer for good cause shown.