The problem with windshield wipers randomly turning on was common on these cars when they were relatively new. Right after my neighbor bought his 530i I remember him showing the car to my dad and the wipers all the sudden turning themselves on. I believe the car was doing other weird electrical things too... If I recall I think the dealership replaced the GM. Now mind you, I was about 8 so I don't exactly remember what the problem was and wouldn't have registered the term "general module," but GM would be my bet.
*waiting for experts to chime in*