BMW calls for a 16W bulb in those positions - looks like a 921, but may not be the same
16W bulbs are not available in local auto parts stores. BMW #6 32 17 160 935 - Tischer lists them for $5.98/ea
You should have (2) brake bulbs per side in the outer tailights - they are the two beside each other on the very top of the module. Brake bulb in the inner trunk mounted lights are for the brake force lights.
I had an intermittant error code for brake bulb in my 09' 328 - found it to be one of the brake bulbs on PS lite. Took the bulb out, it was not burned out, put it back in, and it worked fine for a while. Still get intermittent error - called SA and talked to him about the known problem with the modules - he of course stated that problem was only related to 1 series and he never heard of it in a 3 series.
I grow tired of arguing with those bastards so I just bought a new module from Tischer for $19 and haven't had a problem since...