I have a client using 3.5.1. I have tried all the various nofollow plugins. The only thing they have worked for is the signatures and they do not work for links already posted in the messages. Is there something I am missing? Is there another file parsing the URLS in the body of the posts?
I think you will need to rebuild the links in your existing posts after you have added the nofollow plugin otherwise the earlier posts won't be updated, you need to go to AdminCP > Maintenance > Update Counters >
Ought to mention I'm using 3.6.8 so I'm not sure whether this is the same in 3.5.1