The problem with the fuel filter on the E70 is it is part of the fuel pump.
I have no hesitation in replacing the fuel pump at this age as I do not trust BMW fuel pumps to be reliable past year 8 anyway. The fuel pump was one of the first things I changed in my '08 4.8 E70 when I purchased it.
Also the fuel pumps are having problems with the connector pins melting anyway, just search and you will find some good examples with pictures.
As for the code, I have not see this, but most vehicles have a hard time running Rich. Most things as they degrade lead to Lean conditions.
Suggest you invest $30 or less in your own OBDII scan tool. Get OBDFusion for your phone or tablet, this is less than $10, then get the appropriate wireless interface. Then you can actually Log things like Fuel Trims and Engine Fuel System Status to see what is going on. If you know what to look for, you can even see how healthy the catalytic converters are.
One thing I recently found is these vehicles WILL NOT give an indicator at all when the alternator is not charging. You can use this App to monitor Charging Voltage, but suggest you read this thread to see what I ran into -
http://www.xoutpost.com/bmw-sav-foru...tem-issue.html
You need to gather data and analyze what is going on and hopefully this will lead you to a conclusion as to what may be happening.