I am not sure how the BMW is made.
One of my old mentors now passed was mechanic. He was one in the Army before he got out and open his own shop in civilian life.
So when a lady customer of his came in, upset, as hubby was at 2 week Summer drill...well seems the service station attendent checked the oil he added some. So many miles later the light comes on. She raises hood and sees the oil cap missing , this a Chevy Small block. She stuffed a Burp cloth in the hole. I mean she is a new mom, baby and hubby is away for 2 weeks.
Mechanic calmed her down, told her this is not the first time he has seen this. Shared one time was some ranking officer in the Army lost a oil cap and shoved a rag in the hole.
Mechanic asks me get into the car, He takes a small snake like used in a drain, tiny one with a corkscrew end. He snakes, I let engine run and shut off as he yells to me 'start, shut down, start".
Him working the snake, the engine running...cloth came out. Gas station found the oil cap, top off oil and good to go.
Now engines may differ, might work, worth a try. Mechanic did it, said he had before.
If you get what you feel is "most" out, still uncomfortable. AutoRx is supposed to be safe engine cleaner.
http://www.auto-rx.com/ Stuff happens. No snickers or grins from me. Life is just that way at times, Murphy don't help either.
Best of luck. Engines and Car stuff is NOT inexpensive. Hence the reason I do not make fun of stuff like this.
Let us know what you learn, we all learn from stuff like this.
Regards,
Steve