Hi Rick,
As an administrator, your posts/questions re: the old forum suggest that you see a possible upside in retaining the dialogue on the old forum, especially (I infer) if shutting it down will cause that lively discussion to move elsewhere. Yet you say the old forum is a headache to maintain.
Why not create a new "old forum" on this platform, with the same anonymous privileges now extant on the "old forum" - (except you will be able to find out who the truely egregious violators are.) Let it remain as ... er... freeform as it is now, and use the "forum description" to advise about the content. You could even switch on the "I am over 18" checkbox, to provide an additional fig leaf.
Import the last 5 threads on the old forum, using cut'n paste methods, since 20 posts doesn't justify paying for an import.
You're all done. Best 'o both worlds for you and for the hardcore (no pun intended) "old forumers"!