12.19—Counterclaim.
A registrant may, at the time of filing an answer to a complaint, set forth as a counterclaim: (a) Facts alleging a violation and a request for a reparation award that would be a proper subject for a complaint under § 12.13 of these rules; or
(b)
Any claim which at the time the complaint is served the registrant has against the complainant if it arises out of the transaction or occurrence or series of transactions or occurrences set forth in the complaint.