I think I've got it under control (wouldn't you know I'm doing a state inspection on 12/28 for Dec 2012?)--the error was cc-id 134. I pulled out both carriers, and moved the brake light bulbs from right to left, and the code changed to cc-id 136. So I'm pretty sure it's the brake lamp bulbs, nothing else (although of course, all the bulbs actually work).
I'm hoping that later today I'll pick up 921's which as far as I can see are w16w equivalents, and that the 921's cause the error to go away. Personally, I've always found it funny that Euro cars have bulb failure warnings before the bulb actually fails--it's like Tom Cruise in Minority Report.