While this thread has taken the road of no return to the original topic - and - I haven't read any posts about the window regulators, but I do have a friend that said he replaced two on his BMW. I also deal with electrical issues several times a week.
You need to consider -
As with any electrical issue, but especially an electrical component with a load. Electrical connections have a tendency to overheat and loose contact. A dealer is more likely to replace a window regulator then repair a connection. If you do the repair yourself, inspect the connections before just replacing the component.