My mother in law's BMW was expereiencing the same
problem, and it turned out to be the ignition switch.
But it only drained the battery when the key
was in the ignition. So if she pulled the key
out, no current draw. She keeps the keys in
cause the car is parked in a locked garage.
Poor thing has to pull the keys out now and drag
them inside.
Have you tried measuring the current with the
key in, and also out?
Just a thought.