[Double Venom]

True,
If you have the ability, change the switch to mechanical! If you want to keep it as is, you can find it at NAPA. If it actually screws into the Master Cylinder then it may in fact be a BMW part.

May I suggest before you do either have someone press on the brake pedal...just once and hold. Run a continuity test across the pins, got tone? Not the switch. No tone, have your helper pump the breaks and test for continuity at the same time. Got tone now? Bleed the brakes. No tone...replace the switch.

DV...It's nice to run into a simple problem once in awhile.