The Director, the Director of Industry Operations, or the administrative law judge, as the case may be, may, as to all matters pending before him, in his discretion reopen a hearing—

(a) In case of default under § 771.67 or § 771.68 where the applicant, licensee, or permittee failed to request a hearing or to appear after one was set, upon petition setting forth reasonable grounds for such failure; and

(b) Where any party desires leave to adduce additional evidence upon petition summarizing such evidence, establishing its materiality, and stating reasonable grounds why such party with due diligence was unable to produce such evidence at the hearing.