Over the years I've used Permatex RTV in Orange, Blue, Black, and Gray. They all do the job with minor differences. One is better for contact with fuels, one is better for high heat applications, one is safe for O2 sensors, etc.
Read the label carefully, but I think that most recommend a thin layer on both surfaces, then finger tight on the bolts, then final torque after the silicone has firmed up.
Don't use too much or you get lot's of excess squeezing out of the joint, sometimes in places where you don't want it.
I don't think it's important to use the exact brand recommended by BMW. Just make sure the stuff you use is correct for your application (oil, fuel, water, air, heat, etc.)