*Sigh* I'm finally breaking down and going to a BMW service dealer to fix it. Attempted the self fix to the degree of success for about 2 weeks, then the damn thing popped out again.
I theorize now that once the window falls off track and bends the regulator arm, even after you perform your "fix", when you slam the door too much, the regulator arm is still bent. The regulator arm is now pulling/pushing the bushing in the track off axis under tension, making it easy for it to pop back out.
The chilton's guide I bought says that you can drill the rivet out, replace the regulator and bolt it in, using an M6x10 bolt, washer and matching nut.
No reason why you can't take out the regulator, put it in a vice and straighten it properly, then bolt it back in! (?)
After toying around with the door for two weekends straight, I'm ready to pay to have it become someone else's problem. (so I can go back to THEM if it goes wrong again). (and also quit embarrassing myself at the drive through.......)
P.S. The mechanic smell is White Lithium Grease.