OK, I'm sure this post has been up here many times before, but if there was ever a time for it, it's NOW. Just look at the latest spammer: TavatasareB. He's posting massive spam on every single thread he can, and it's not just one line, it's pages worth of CRAP. If this were a forum with only 10 visitors on average, that would be one thing; but it's not. The Main FFXI forum regularly has at LEAST 100-200 visitors, and I've seen 1000-3000 on more than one occasion.
For a spammer to go on for so long and in this magnitude, especially with 1000 current viewers suggests a slight problem. So I would humbly suggest what has probably crosses your mind many times: get a specific moderator or 5 for that forum, and quick. It really needs it.