Administrative law judges shall perform no duties inconsistent with their duties and responsibilities as such. Administrative law judges may be assigned duties not inconsistent with the performance of their functions as administrative law judges. Save to the extent required for the disposition of ex parte matters as required by law, no administrative law judge shall consult any person or party as to any fact in issue unless upon notice and opportunity for all parties to participate. The functions of the administrative law judge shall be entirely separated from the general investigative functions of the agency. No officer, employee, or agent engaged in the performance of investigative or prosecuting functions in any proceeding shall, in that or a factually related proceeding, participate or advise in the administrative law judge's or Administrator's decision, or in the agency review on appeal, except as a witness or counsel in the proceedings. The administrative law judge may not informally obtain advice or opinions from the parties or their counsel, or from any officer or employee of the Alcohol and Tobacco Tax and Trade Bureau, as to the facts or the weight or interpretation to be given to the evidence. He may, however, informally obtain advice on matters of law from officers or employees who were not engaged in the performance of investigative or prosecuting functions in that or a factually related proceeding. This limitation does not apply to the Administrator, and the administrative law judge may, at any time, consult with and obtain instructions from him on questions of law and policy.