vansdonk
That's not buffing out
Well, they can run without ever having an oil change, but not run on water? 

Fwonk that... Drain the tank, blow out the lines with compressed air, change the fuel filter, fill the tank with fresh gas and some dry gas and you're good to go. Under $100... Maybe $250 if you let a shop do it. (Not counting the cost of the fresh gas)
i would say with bmw's ridiculous pricing on service 12k sounds about right to replace the engine and entire fuel system. even though that is not needed, i bet a good draining and thoroughly cleaning the fuel system it would run just fine
Just use E85!
Enough alcohol in that to keep things dry.