POR 15 is a coating, and the alternator has coated wiring in it. I am thinking that wont be your problem.
Better go back and check the wiring connections, you got a heavy gauge wire crossed up somewhere.
We dont get many BMWs in here, but welcome anyhow.
You also could have a pinched wire (heavy gauge)
You can allways unhook the alternator completely and test the car to see if condition goes away.
Fact is stranger than Fiction