In addition to some fairly sizeable core software upgrades, I've installed a new module to handle the private forum functionality on the site. This replaces the old Groups module, which was insecure and cludgey at best. On the backend, I'm now able to set forum access by role or user, meaning plot members will be able to see all group forums automatically and individual user accounts can be assigned to those forums as well.
Unfortunately, group leaders can no longer manage their own roster, but that's a small price to pay for a system that broke down with some regularity, leaving private plot posts exposed for the world to see. The new module is tighter, more focused, and better supported, so I'm confident it will work better for us going forward.
If anyone notices anything amiss, like forums you ought to have access to (or not) that you don't (or do), please let me know.