As a Star Trek fan specializing in finding background actors and extras this is an extremely exciting thread. Thank you for your findings! I don't know of any more appearances by Basil than listed here, but I will keep an eye out.
Browny: If your documents lists Basil in Obsession they are more detailed than anything I've seen before. It would be very cool if we could get more information from them into the Trek community!
Heh... looks like this information is filtering out into the world.
Not only is Basil credited on the STAR TREK site http://memory-alpha.org/ for ERRAND OF MERCY, PATTERNS OF FORCE and OBSESSION - there's a link to this very thread!