Thanks to Keith Furman and Michael Tsang for the tip: Netscape Communications has released a maintenance version of its Communicator suite, version 4.51. Communicator 4.51 adds a new version of the AOL Instant Messenger (version 2.0), some security fixes, and a couple of bug fixes.

I tried to find an "upgrade" version of this via Smart Update but was unable to do so. There are several full version downloads now available, however, from the Netscape FTP site