The only way to force BMW to fix it, now that they have changed the fuel sender, is to report it to the government as a safety issue. if they get enough complaints, hopefully an investigation and then recall can be forced.
If everyone with the strip fuel sender issue would file a complaint ...
NHTSA Safety complaint site
I have had a dealership tell me that it is the ethanol in our gas. No one seems to know or want to find out -- except we who were crazy enough to buy one. (I am on sender # 4 or 5 I've lost count.)