I have just got my F20 back. I took pictures of the rust and provide them to my dealer.
I am pleased to say that the rusty stuff is gone and a clear coat (sealer) by BMW DE has been applied.
The metal is still the same colour but without the rusty spots.
I was informed that the work is guaranteed for 10 years.
As for the Stop/start
It is now set to the mode I have it in when I turn the engine off.
I am very happy that I can now turn it on or off as I like and it stays that way.
Having to pay to have it done did not impress me.