I am happy to say that the new procedure for manually approving new members has been very effective at controlling spam. All of the spam posts since then (and there have not been very many) have been spammers coming back to use account entered before the procedure change. There may still be some of those from time to time.
A downside has been that a few -- I think only 3 if I remember right -- legitimate members have been delayed in having their accounts approved. This can be because they either don't email me for approval, or once or twice I have missed the email the first time.
However, we still have 5-10 spam bots trying to register on the forum every day. Many with Russian ISPs. The volume is crazy!